If you have a non European passport then you can buy a Eurail pass. There are different types of passes.

Flexi passes are valid on a specific number of days within a certain period of time, like 4 days within one month. Then you can travel on 4 days of your choice within one month. 

Continuous passes are valid for a certain period of time, like 15 days or one month. Then you can travel on every day during the period. 

I have another question. How would I plan a trip. Do I have to pay for resevations? 

Please first have a look at the information available, such as:

https://www.seat61.com/how-to-use-a-eurail-pass.htm

And:

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

Then come back with specific questions.

For questions about booking a reservation, please always mention at least route, date and departure time.