2. Reservation fees depend on the trains you'll use. For an overview (and how to book), have a look at:
   https://www.seat61.com/interrail-and-eurail-reservations.htm
3. Possibly some trains were included where the pass isn't valid. If you want to know more, you'll have to show the exact trains.
   In addition, please don't plan with the Interrail/Eurail website or the rail planner app. They're not reliable. Use national websites/apps, or bahn.de for international journeys.

thanks.
but still it looks like a mystery to me (maybe because i am old … ). They tell me now on some connection (Madrid > Lyon), that e.g. i need to make a reservation at the station in spain. how should i be able to book this train than from germany? 

Who is "They”?

The direct train Madrid-Lyon can be booked via Interrail or via Happyrail, see the page on Seat61 I mentioned. If that doesn't work for you, then please mention your travel date.

About the outbound trip: you’ll have to pay separately the Paris-Est - Montparnasse transfer as well as the Hendaye-San Sebastian Euskotren. Only costs a couple € each.

Whether a pass + reservations or standard tickets are better value depends on the travel date. At short notice the former is likely cheaper.

Thanks so far. That helped. I am a little further now.

 

What I sill don’t understand:

1. When I search for a connection via Renfe (e.g., Madrid to Montpellier on March 7th, 1:25 PM to 7:52 PM), the ticket costs €95 all-inclusive. With the Interrail Pass, I have to pay a €35 reservation fee for this route. Am I understanding this correctly? (This raises the question of whether the Interrail Pass is worth it for me in the end as pointed out above)

2. For AVE trains, I get a message saying, ‘Seat reservations must be made at the station (more info).’ Does this mean I can only book the reservations on-site? And how much do these reservations cost?”

and 3rd is more a suggestion. I need to go from Madrid to Munich from 7.3. to 9.3. and looking for a nice stopover 2 nights in a town on the line (everything beside Paris. and somehow roughly in the middle that the trip is nicely done in 2 days).  i was thinking about Lyon or Montepellier. but i cannot figure out some smooth connections. Any other recommendations?

1. Madrid 13:25 to Montpellier is an AVE. Reservation is €10 in 2nd class, €13 in 1st, plus any booking fee.
2. AVE trains all have the same reservation fees. For domestic journeys, there's also a Premium option (1st class with food) for €23.50 plus any booking fee.

This is from the Interrail website, as an example:

On which website are you seeing “Seat reservations must be made at the station"? If that's on the Rail Europe website: that's their standard message for a mandatory reservation you can't book via Rail Europe. They can't book AVE pass reservations. Please follow the Seat61 reservations page as a guide:

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

i did this on raileurope (but same feedback) - so i cannot do the reservation. I unfortunately cannot miss this one. (and yes, you seem right and it would be 10 Euro)

Not on raileurope.com, but you can on interrail.eu.

excellent

now i still need to figure out, if the pass with all the reservertion fees really is worth it :)