You might want to read through this forum, getting info on how to get the tank ready for fish with a *fishless cycle* which is the more humane method; and remind yourself, if you were aware before, about the ammonia, nitrite, and nitrate cycle of the water. If this is all unfamiliar, just ask, and we'll gladly give you the low-down.
Do you also have your friend's filter, heater, etc, or just the tank? Does it have a lid, and lighting?
We here love playing with ideas for stocking the tank. But first, you need to get the tank properly set up (and that includes making sure the healthy bacteria in the water is established). Another resource and a great place to figure out what fish are compatible in your tank is Aqadvisor:
AqAdvisor - Intelligent Freshwater Tropical Fish Aquarium Stocking Calculator and Aquarium Tank/Filter Advisor
Oh, and welcome to myfishtank!
Cheers,
Laura