By covering all aspects of thegame it makes it a enjoyable experience for anyone, with functions for anything from practice and public fun to competitive matchplay and shoutcaster functions. Promod is game modification for Call of Duty promoting the competitive side of the game. I really don't know what this does but I guess it's just some minor bugfixes.
The next patch you will need to install is patch 1.7. This is because the game is already patched to 1.6. If you bought CoD4 GAME OF THE YEAR EDITION you will not need this patch. This patch contains the custom maps that was realesed by IW. The first patch you need to install is 1.6. However, you will only need to install two of them. This is because your game isn't patched.ħ patches have been realesed.
You start the game, create your profile, try to join a server, but you get an error saying: 'Server is another version.'. Assuming that you've just bought the game and you wish to start playing instantly.