You can think of it as your own personlized library of chess games of your favourite masters of the game.
The free part of the app contains almost all of the games by Kasparov, one of the greatest players of the game with more than 2000 games spanning his entire career.
If you want you can then buy addiotional game packages with almost all the games of great players such as Karpov, Fischer, Tal, Capablanca, Euwe, Aljechin, Botvinnik, Smyslov, and more. (and more will be available in the future).
You can analyze the games with an engine or simply play through them and analyze yourself.