hey bro,
you buy them from the black market. I forget what catergory they are under, but have a good search and you'll find them. Make sure they are equipped in your inventory before going out on the mission.
They work automatically when you have them in your inventory, you don't need to do anything just use the terminal as normal and the EMP will do it's thing.
otherwise why can't you do the hacking minigame? it's not that difficult..
Good luck