Where on the unit do you put the coolant?

Sorry, but if you do not know this, I assume you are not licensed to be handling refrigerants, in which case you are breaking federal law. There should be a port with a dipstick that says "add coolant here". Just get yourself a funnel (coolant approved of course) and dump the stuff in until it shows full on the dipstick. Or better yet, hire a licensed professional to do the job for you legally. Good luck on your project.