If I have the Altitude and the Azimuth of a given lat/long and I have to launch a satellite from that given point on Earth. What value do I put in GMAT NASA software to get a simulated orbit?
I believe the information you are providing is not enough. Do you intend to simulate the launch? Do you intend to simulate launch and the orbit, or just the orbit?
If you want to "observe" the evolution of your satellite for a given orbit you require enough information to position your satellite (Epoch and Keplerian elements - your altitude and azimuth are included here but not enough-) in time and space, and then you need to define how to simulate the orbit (propagator) in terms of masses attracting your satellite, and mathematical model.
I guess a good starting point would be the GMAT help.
In order to undertand Keplerian orbital elements I recommend the book "Satellite Technology Principles and Applications" from Maini and Agrawal.