Hi and welcome to the DIS! It can be a little overwhelming to start planning a trip with all the grat info here, but the great news is the CM's at reservations are so friendly and helpful! That is my first advice, when you call, be cheerful, excited, polite and all will go well. I usually call 1-800-828-0228...and express that I am calling to make a "room only" ressie. This is the type of ressie that allows you to cancel up to 5 days out w/no penalty. After you give info to CM tell them which resort you are hoping for and after you are given the rate ask to apply the code you have. They are used to a ton of codes and it is not a problem requesting them. I would ask to make sure if you need any ID or such depending on the code you are using...such as if you are a Fl resident etc. ask for a written confirmation to be sent to you. You should have 10 -14 days to apply your deposit which is 1 nights stay plus tax.
All will gi fine. If your dates are sold out for the rate you need, ask them to check what the best hotel/rate is you can get for your dates, or try back again often.
Good Luck!
Pam