Interrail has a couple of different tickets. They are explained here so that you can decide which would fit your needs and interests best.
If you live outside of Europe, you cannot travel with the Interrail pass. If you still want to travel Europe by train, take a look at Eurail. You can however travel with Interrail if you prove that your place of residence is in Europe, no matter your nationality.
The Global Pass
With the Global Pass, you can travel all of Europe. It allows you to visit up to 30 countries in Europe with just a single train ticket. However, with this ticket you can only have one inbound and one outbound journey from and to your home country.
The One Country Pass
With this pass, you can travel one country in Europe, but you can choose your destination from 31 countries in Europe. Here too you can only have one journey to and one journey from your home country. This pass is usually a little cheaper than the Global Pass.
Are you still not sure which pass might be the right one for you? Try using this interactive search tool provided by Interrail.