Hello from a new user

Hello, my name is Kristina and I am new to fitbit. A friend of mine just gave me the flex model as a birthday gift, and I am just getting started. One question is how do you record the pace using a treadmill? It allows incline and duration, but if don't understand how to use the pace feature. I walked for 25 min this morning on a treadmill at 3.0 mph and a 4.5 percent incline.