Hi Ron,
Big question this one as Tom said it will depend on what you want to spend.
How do airbrushes work.
When you press the trigger you will get a flow of air though the brush onto what you are going to paint: if you add paint it will atomise the same as pixels which make up a TV picture and settle on your model. There are a lot of airbrushes to look at but if you are just starting keep it simple and cheap.
So what types are there.
They all have three features and that is (were atomisation occurs)this can happen in two places outside of the brush this is usually in a jar container under the airbrush this is called siphon or bottom feed.
You can buy Gravity feed with this one the paint will be contained in a cup on the top of the brush usually by a screw or push fit, I use gravity fed which I find are more capable of fine detail work reason is less air pressure required to get paint from the cup to the nozzle that on other feeds systems due to the lower air pressure plus you use less paint.
What type of action?
Single Action that is when you press the trigger and air and paint both start to flow together.
Double Action when you depress the trigger on a double action you only get air, when you pull the trigger back you get air and paint, bit tricky to master at first Ron, you have to learn over time but I think you would end up with this type, a good brush to buy of this type is the Iwata Neo this is a start up brush for the early stages, have a look on E-Bay you may be able to get a Neo with compressor or similar.
Final Points.
Ron
By now you have a few things it think about,in the main it is all about how you wish to use it and of course the price you won't to pay, and a final point is spare parts.
Hope this is of help to you.
Regards
Trev
Work in progress: Tombstone (Scratch) - San Francisco 2. -The Mayflower ( scratch by plan).
OcCre- Santa-Maria (Kit).