Explaining the difference between an air regulator (which is designed to control airflow - which is measured in Cubic Feet per Minute - CFM) and a pressure regulator which is designed to control air pressure (which is measured in Pounds per Square Inch - PSI) gets rather complicated.
Since I rather doubt that you intend to operate several high consumption air tools with your air compressor, you don't really need to worry about what your CFM usage is. It doesn't take a whole lot of CFM for an airbrush to work, so what you need to worry about is your air pressure which means a pressure regulator.
You don't need to buy a large regulator, there are several different brands of mini regulators out there than be bought for $20 and up. And if you want, you can spend a few extra bucks and get a combination regulator/moisture seperator unit (which is what I recommend). And make sure that the guage in the unit reads in two pound increments. Most regulators come with guages that read up to 200 psi and are calibrated (marked) in 5 lb increments. For 5 to 10 bucks you can buy a guage which goes to 100 lbs and is marked in 2 lb increments. This lets you adjust the air pressure much more accurately and quicker.
Hope this helps a little - good luck