1. useing primer will help the paint to stick
2. using tamiya masking tape will help a lot
3. removing the tape before paint fully dry will give you better result
4. acrylic paint (mainly testor) are very fragile, use enamel or lacquer if you plan to use tape.
5. Thinner is used to clean your airbrush and thin the paint (acrylic might be ready to airbrush, but other paint need thinner to be airbrushed) If you don't know what thinner is, maybe you didn't even cleaned your airbrush, and those cheap airbrush don't like eavy stuff, so maybe you airbrush is already dead
You need to fully clean your airbrush everytime you use it with proper thinner
6. a cheap airbrush will not give you many fun
if you want to learn and having fun, a good airbrush is way better than the cheapo airbrush that use air can (that will cost you even more than a spray paint can anyway and give you really bad paintjob compared to spraycan) a good airbrush cost 50$ (price of a ferrari enzo is some ripoff store !)