CS= counterstrike usually referring to counterstrike: 1.6 while CSS means Counterstrike:Source
CSS is better than 1.6 because it runs off of the source engine allowing for some good physics and graphics.
CSS costs 20 usd ONE time payment and is much MUCH MUCH better than warrock, you can host your own servers and stuff or join other hosted servers. Servers have their own mods like regular getting hosties or planting a bomb, Deathmatch, Gungame, Gungame deathmatch, Zombie Mod, and other user created mods on countless offical and custom maps, you can skin your weapons to your liking and if you know how to use the tools provided in the source sdk kit you can make your own maps :O