everybody's different, but you dont really need a lesson if you have a little patience and time to play with your brush. i bought Osprey's "how to use an airbrush" and it really didnt help much if you want to know the truth. it even said in the book to start spraying paint through the airbrush asap and get the feel of it. logging time on the brush is the only way to learn. hands on my friend, you cant buy experience!! what type of airbrush do you have? is single action or double? are you gonna use it for modelling only? have you tried it yet or, are you waiting for lessons first? dont be afraid my friend, its an excellent modelling tool and it will only do what the user manipulates it to do.
if you have a double action brush, load some properly thinned paint into the paint resevoir ( about 60% paint / 40% thinner is a good starting point ), assuming that you have an aircompressor with a pressure regulator, dial it to about 15 psi. assuming that you have the hose connected to the compressor and airbrush, push down on the trigger located at the top of most airbrushes to start the airflow, and pull back to start the paint flow. my osprey book said to take a piece of graph paper or draw a series of dots with a pencil on a sheet of paper and target practice hitting the dots with the brush. when you get fairly consistant with that excercise, try to get the same size dots each time ranging from large (which incurs backing the brush away from the paper about 4 inches and pulling a little further back on the trigger) to small dots ( obviously get about an inch from the paper and dont pull back so far)
also, in the osprey book, it says to began painting on 3D items like coke cans or beer cans or discarded kids plastic toys and such. paint something 3D is totally different from paint a flat piece of paper. if you have any questions, this is what this forum is for. there are plenty of knowlegable people here that can lend a hand. later.