One of the main train stations in Warsaw, Warsaw Wschodnia (Warsaw East) has plenty of tracks leading all over the country, and it's the easiest place to pick up a train if you're staying on the east side of the river. 

There are essentially two sides to this station, with tracks located in the middle. Whichever side you enter from (North or South) will have either ticket machines or windows where you can buy train tickets. Then, use the screens (which display train times and tracks) to find your track! It couldn't be easier 

Warszawa Wschodnia was built in 1866 as the terminus for the Warsaw-Terespol line. The station building was destroyed during World War II and the current one was built in 1969 when for a while it was considered the best station in Poland...until, as with most buildings in the Communist era, it fell into a sorry state. This all changed when it was renovated in time for EURO 2012 and now it still serves international, long distance domestic services and suburban train routes that travel from Warsaw Central (Warszawa Centralna).