Basically what you want to do is add -developer to the end of the game shortcut.
For example, if you have a shortcut to FarCry on your desktop, right-click on it and look in the 'target' box, there you will see where the shortcut points to (I'm using Max Payne as an example):
Not what you need to do is to type '-devmode' (here I've had to use -developer because the game is different) with a space between it and the target so it looks like this:
Click on 'Apply' and then close the window. The next time you load the game, press the '` button (it's the left of the No. 1 key, above the TAB key, and under Esc) in the top left of your keyboard during gameplay. This will bring up the console, allowing you to type in cheats, then all you have to do is press that key, type the cheat, press return, and then press the console key again to close it.
Happy Gaming.