First you press control+shift+c all at the same time, and a little box will appear at the top of you're screen. Then you pick the cheat you want to use and type it into the box.
A really good cheat to get money, is to type 'Motherlode' and press enter. If you have done it right, you'll get 50,000 simoleons!
For more cheat codes see the related link below.