RES are only needed for some 10% of all trains that run in the whole of EUR. Just like in Canuckyland: VIA must be reserved, but GO-Ontario, The Vancouver Skytrain-or whatever-its just: anyone can board, there are no checks, and if its a very busy time and all seats are taken when you board (its not like a plane-trains will make multiple stops on their route and on most lines there will be a train ev hour at the same times):then you stand-till next stop when many will get off-or not. OR if you´re too shy to command people to take that lazy luggage of their seats.

BUT about all newcomers to EUR all seem to want to ride exactly those routes that require RES and also hard to get. Not that imaginative….

In such cases you do it-best by the other way as listed in a long overveiw by seewulf, linked to by anna B fra Sverige in her welcome postings. This RES indeed garantees there is space for you-it may also mean you can chase some ignorant type who did not check away from your assigned seat.

Passholders (and most are by INterRail-those who live in EUR) only make a tiny fraction of the pax that usually sit in a normal train-except for some specific INTernational routes. Many conductors have not seen people on a pass for weeks.

In general it seems that those who are very unused to ride trains make many more problems as there really are-you will learn how it works in a very few trips.

If you don't have a reservation, then you have no confirmed seat. That's how most trains work. You create the ticket in your app just before boarding the train and then you just look for a free seat on the train.

Here is some useful information from the experienced travellers in the Community regarding both planning, reservations and activation of pass and travel days. 

 Planning

The rail planner is normally not up to date, as it only is updated once a month, so to be sure of the time table you better check the timetable and availability on the websites of the national railways. The bigger national railways, like DB (Germany) SBB (Switzerland) and ÖBB (Austria) cover several countries. 

 Reservations 

The quality of these replies is outstanding! 

Thanks for all the information. What tripped me up is that you seem to be able to book the route using third party services in which case I’m thinking you do have a reservation for most trains, but some are just unable to be reserved? 

In any event I can avoid all the routes that require a reservation easily and intend to. 

I’ve been to Europe before, but I’ve never bought one of these passes before and intend to pack my days so I’m really just trying to see how I can minimize this risk. Sounds like get there early and reserve what the app suggests are the answers. 

There are very few routes where there only are trains with mandatory reservations except for Spain and the Eurostar between the UK and mainland Europe. In France, Italy and Sweden there are mandatory reservations on high speed trains, but there are almost always slower regional trains on the same routes that you can use without reservation. 

Where are you planning to travel?

I’ll be staying in Amsterdam and going to Belgium and Germany. I intent to sleep in Amsterdam each night so I don’t have to haul my stuff around and can spend the whole day exploring and then make it back to sleep. The key being making it back to Amsterdam each night to sleep. I’m not in Europe long as I’m here for another purpose, but I’m extending my stay to travel for a few days. 

If you only will be travelling in the Netherlands, Belgium and Germany there is no need for reservations as you only will be travelling by day trains.

Except possibly thalys and eurostar from Brussels and Amsterdam 

Eurostar stopped selling NL-BE journeys.

Thalys is too expensive IMO for NL-BE journeys. I always use the hourly intercity train.

Knowing that the rail planner is typically not up to date is a very handy piece of info. I cannot seem to get my hands on the train times for those intercity trains I'll be taking. Amsterdam to Brussels they are IC 9212 and IC 2030. Back from brussels it should be the IC 9263. Going to Germany I’ll be taking ICE and RE and possibly SBA and RB trains too. Where is the recommended place to look for up to date time tables for all of these trains? 

Bahn.com is a good place to look for those trains.

If you want real time information on your trains and connections you should consult the respective railway apps or websites.

DB Navigator for Deutsche Bahn trains (ICE - RE - RB and all the sorts): https://www.bahn.com/en

NS (for the Dutch railways): https://www.ns.nl/en

and NMBS (in Dutch) or SNCB (in French) for the Belgian Railways: https://www.belgiantrain.be/en