Using the program is not all that easy, which is why as soon as you run it the first time it gives you the option of getting a full tutorial that explains exactly what it is you need to do.
Now, not only are you able to use cheats in order to pass the game more quickly, but you can also modify some important parameters in order to, for example, reduce your character’s life if you feel it’s a little too easy. Once it’s running, you select the game’s executable file which then gives you the option of editing some important variables, such as the number of lives, or any other modifiable parameter. In order to use it correctly, you have to run it before launching the video game and leave it running in the background.
Cheat Engine is an open-source tool whose sole purpose is to help you use tricks and cheats on your favorite video games, therefore allowing you to manipulate and change all sorts of parameters on them.