Imagine a bird floating in a lake. In order to take flight, it has to make a flying start. It has no other choice. It cannot make a running start, because it cannot run on water. Some birds are not strong enough to fly off of water. To take flight they must move to land and make a running start. For humans, it means to suddenly start doing whatever it is that you wanted to do, without any intervening warm-up.

This means that you have gotten a good start, and the start to what you are doing is positive.

The whole Idiom might be "get off to a flying start" or "get off to a flyer" as well. It means you have a very good start.