After you type in the cheats yes you do press enter.
Press Ctrl + Enter
press insert
Press enter type the cheat and press enter again
at the press start screen .don't press start
You simply press start, select options, then you enter the code.
You can input cheats by going to options section (on the main menu) and selecting cheats/codes. Press the X button (for gamecube) to enter the cheats that you find online. If you have the PS2 vesion, then I don't know what button to press. My guess would be either Square or circle.
All you have do do is press ~ and then enter a code.
Press ` and type your cheat
When in the menu, press ctrl + w.
press p, then enter desired cheat
Dude, just google "GTA IV cheats" and enter the phone number into your phone in the game(press "up" twice on the D-pad).
just press some buttons