There is a map of the main railway lines, but there are so many trains and lines that it is not all on it, and also in some parts wrong due to works or cancellations some lines are closed at the moment. But it is helpful for a first overview.

https://www.interrail.eu/content/dam/pdfs/Interrail%20map%202022.pdf 

For planing you can use bahn.com or fahrplan.oebb.at for planning in most places in Europe or the websites of the train companies that run the train. 

Keep in mind that some trains need an additional reservation to board. You can find an overview where you can reserve here: 

If you have further questions don't essitate to ask!

Compared to AmTrak/USA you can safely assume that ALL cities and most smaller towns have a trainstation and hence can be reached on the rails. For the tipical tourist destinations that are not always in towns-an old-fashioned thing like a guidebook might help-or the new-style google.

Geografical restraints may in some cases mean however that there is not a direct line where you may expect this-a mountain or lake is in the way.

Or use the various routings that are presented in general section as guide and make own variations-these are made with good connections available.

However-following this forum it wil transpire that about 99% of newbees all want to stick to the same boring routes-often exactly those with hi-speed train that are hard to get RES on and also want a hefty surcharge for that. Noone eve seems to get the brainwave that s/he is not first one and that all questions have been asked here dozens of times

Just to show you the complexity of your question here is a link to the network map for the North of England.

https://www.northernrailway.co.uk/sites/default/files/2022-01/Network_Map_261021_1_0.pdf

Obviously there are many network maps for operators across Europe.

Re start and finish stations of a train’s routing if you search for routes in any planner (There are many) they often give the train number they show. They may have a prefix (IC, EC, ICE etc)

 A quick search on Google with the train number often reveals that train’s full route and stops on the way.