Compare prices : advance tickets could be cheaper but it mainly depends on the Eurostar fares.

The flexibility Eurail passes usually give won't be doable this summer I'm afraid. You'll have to book seats in advance whenever required.

Eurostar trains have a 30€ Eurail passholder seat reservation fee. There's also a passholder quota (pretty much unique in Europe).

If you choose the Eurail way you'll need in any case a Global Pass if you intend to go to London.

Feel free to read these links : https://www.seat61.com/how-to-use-a-eurail-pass.htm

https://www.seat61.com/interrail-and-eurail-reservations.htm

Hello and Thank you for your fast response, so I’m assuming that’s better to buy The Eurail Pass becuase most of the days we’ll exploring France and the Basketballs Games at the Olympics. So instead of buying the Global Europass, because we want to visit London, can I just buy a train ticket (normal ticket) and pay wathever the fee is? Or it’ll be cheaper in a long run to buy the Global and use it to travel France and London???? Sorry please help me, so in summary I’ll be staying in Paris France travel to Lille France for Basketball games from Jul 24-Aug 5th, then staying in Paris for the rest of the Olympics between those days is when we want to go to London, hopefully you can help me to figure it out what will be our Best choice, Again Thank you so much, :)

I don't know whichever option will be cheaper honestly!

Mandatory seat reservations for passholders are quite expensive for multiple journeys (extra costs on top of the pass). Check the link I posted above.

Seats are otherwise included in (advance) tickets.

Eurail could allow you to wait until later to book trains, especially if you can remain flexible. Still, I wouldn't count on availability on the day.

You could book tickets to London in advance (really as soon as your dates are set) and then only use a Eurail One-country pass for France. I don't know…

Maybe someone else can share some advice but there won't be a definite answer I think.

Thnak you agin for your fast response, I think it;s better to book my tickets to London as soon I have a set schedule, Now, I was reading and I can buy My Eurail Pass now correct? and it’ll be active the day that I start using it correct? If I buy Only my Eurail Pass now, I don’t have to reserve seats correct? I just hop into the train to Lille and Lille to Paris, or surrounding areas Like the Loire Castles correct? No seat reservation correct? 

Again I’m so happy that you are helping me, I really Thank you from teh bottome of MY HEART 

Yes you should buy Eurostar as soon as your dates are set.

Not really, that's what I was trying to say : French fast and high-speed trains require seat reservations. You won't be able to board without one (or if you somehow manage, you'll get a big fine as it's treated like travelling without a valid ticket).

This limits your flexibility. On routes with frequent trains (such as Paris - Lille) usually you can buy them the day before. However this is not guaranteed during the Olympics I'm afraid.

However you could always travel on reservation-free regional trains : slower and quite infrequent depending on the route.

Paris - Lille is around 2h30-3h vs 1h by high-speed train.

Another example : Paris - Blois-Chambord takes 1h30 by reservation-free regional train but there are only 4 services a day... (a few more via Orléans). Doable as a day trip of course but you'll have to be careful with train times.

Feel free to ask anything.

I’m very confuse now, I thought that I can buy my Eurail pass now so I can travel to Paris to Lille, for my daughters basketball games, we are staying in Paris and we want to go to the games and back, can I buy my Eurail pass now? Can I  travel to the Loire Castles using my Eurail pass or regular subway? 
I already understood that going to London I’ll need the Global Pass. That’s clear, can I use my global pass to go to brujas Belgium we realized that’s very close from Lille????? Sorry for all these questions, I appreciate your time God Bless You 

Of course it’s possible to buy your Eurail global pass right now, if you do know which class of travel you’d like and how many travel days you will need (just count all days when you are planning to do a trip). Just make your decision and you are ready to buy it.

For some of your trips, you do need a mandatory reservation if you’d like to go by high speed or long distance trains trains. So if you did buy your rail pass, you’d have to do some reservations, too. 

Paris to Lille (and back): Fastest way is by high speed train. It takes 63 to 76 minutes. You’ll need a mandatory reservation for this. The price for a reservation is 10 € if you do your reservation early enough (may be 20 € if doing the reservation late). It’s possible to go by regional trains without a reservation, but that takes longer (about 3 hours). 

Paris to London (and back): You need to go by high speed train. It takes 2h 18min. You’ll need a mandatory reservation for this. The price for a reservation is 30 € 2nd class or 38 € 1st class. But there’s a quota per train that may sold out so reserve your seat very early. 

Lille to Brügge (and back): There’s a connection every hour that doesn’t require any reservation. It takes 95 minutes. Just hop on the next available train. The rail pass is your ticket. You need to change trains once.

Paris to Loire castles (and back): As there are many castles, it depends on where you’d like to go. In general it’s possible to go by train and it’s possible to use your rail pass, but you’d need a mandatory reservation if going by long distance trains. So you’d need to plan which castles to visit.

To get reservations, you may use Train tickets in Europe - Search & Book on Rail Europe. Bottom left there’s a line “Add rail pass”. Tap it, choose the rail pass you did buy and you should get the prices for reservations. To buy a 1st class reservation, you do need to buy a 1st class rail pass, too. 

Thank you for your response, So, if I buy my Global Eurail pass this same pass can I use it in France and to Brugee???? ( Burgee requieres Global or just Eurail Pass?) So the Eurail Pass it’s only for France correct? It’ll be cheaper to buy a ticket high speed train to London and back, without buying the Global? 

The regional trains to Lille: Do I need to buy an Eurail Pass? or just buy the ticket and hop into the train?,  of course with seat reservation, also same thing with the Loire castles?

Eurail is a company selling 2 types of passes : Global Passes and One-country Passes.

The Global Pass lets you travel in over 30 countries while the One-country Pass is only valid in the country of your choice (France for example).

Please read this link : https://www.seat61.com/interrail-and-eurail-reservations.htm

You’re still getting a bit confused with some terms I think :)

Eurail pass = train passes for non-europeans.

A Eurail pass comes roughly in two forms:

One Country Passes (only valid in one country) or Global Passes (valid on all participating rail companies in Europe). One country passes are generally a bit cheaper than the global ones.

So if you want to go to Bruges, a global pass is an option.

Another option is to combine a one country pass, with ordinary tickets. For example, the regional trains from and to Lille-Bruges. These cost about 14 EUR single ticket, even cheaper with a youth ticket or 65+ discount (about 11 EUR I think). Get them on the international website of the Belgian railways https://www.b-europe.com/EN . Can be bought about a month in advance.

So buying a one country pass for France, and ordinary tickets to Lille-Bruges are a very good idea and probably way cheaper than a global pass.

Regional trains cannot be reserved in most cases. Hop on with a valid ticket, and find a free seat.

For Lille-Bruges: avoid the TGV services going over Brussels, these will be much more expensive and take a longer, are less flexible and a bit of unlogical route.

Wow thank you it really make sense now, I really appreciate your help and kindness, Now for London I’ll be doing the same thing correct, buying a one country pass for France  and buy an ordinary tickets to London (2days) are a very good idea and probably way cheaper than buying a global pass? Or do I need to buy a Global Pass to go to London? If I buy the Global Pass can I combine it and use it in France?

You’ll have to calculate and compare a bit.

You cannot take Eurostar with a One Country Eurail Pass, only with A Global Eurail pass.

Normally a global pass is good value if you travel in or through 3 or more countries.

The Eurostar (London - Paris/Lille/Brussels/Amsterdam) can be rather expensive, especially during the olympics.

Further annoying thing: the Eurostar has limited seats for pass holder reservations reservations, forcing you to buy (expensive) ordinary tickets once the reservations for Eurail pass holders are sold out. Usually only a problem during peak season times, like Christmas, long weekends and summer holidays.

As soon as you have your dates set, we can help you a bit comparing prices and check what will be most cost-efficient for your plans.

Okay I’ll let you know so you can help me please, Thanks God Bless You