Today is apparently 20 years since Mark Smith, known as The Man in Seat 61, registered the domain seat61.com.
A lot has happened since then and the internet is a very different place today compared to what it was then, but this is still the best guide to train travel there is, not only in Europe. If you have any questions about how tickets machines work, when you should buy tickets, what service there is, or any other train related question, you can probably find an answer at https://www.seat61.com