First run [pec] The Interface (pec.exe)

Click on 'File' and then on 'User Database'

Click 'Add Cheat' then 'New Cheat' will apear in the cheat-list

Change the title of your cheat in the title box (for example : 'game name - cheat name')

Fill out your codes in the text boxes under the code-listbox

And click on add

Repeat those step until you've entered all the cheats you want

Check all the checkbox in the cheats-list you wish to activate

Finally click on the bottom ok, it will close the window

Click "Send Cheats to Plugin" in [pec] and you're done!

Keep in mind that it won't modify the built-in database it adds a user.inf.
If you want to activate your own codes you'll have to select them in the User Database.