How do I do this? Can anyone give me clear instructions.

[Edited by Flamberge, 12/23/2012 6:09:07 AM]

But have you checked the instructions given with the trainer? You can either use it on the trainer itself or by reading the included text file along with the trainer inside the archived file you downloaded.

For example for the safehouse unlocks it says this

Numpad 5: Safehouse Unlocks - use this in the safehouse portion
of the game. It work for the Weapons or the Disguises.
Press the option key and then click on the Weapons or
the Disguises menu item and when the list opens up the
cost for each item will be zero.

If you check the other options then you will see how to use them.