First things first. What is it you want to paint in the long run?
I teach my students a basic philosophy of "Look ahead, and think in reverse." By that I mean, look at what you want to do or achieve in the end, and then look at the steps and tools you need to get there.
There will probably be a few things or steps needed along the way, so working your way backwards from your end goal lets you see what you actually need to get and learn to achieve your goals.
As to the terms, forums like this are a great place to ask.
The following are a few of the terms you will hear bandied about and their meanings;
PSI means Pounds Per Square Inch, it refers to the amount of air pressure, used or needed.
CFM means Cubic Feet per Minute, this refers to the volume of air moved per minute. While it relates to PSI it's not the same thing.
While you can blow a fair amount of pressure through a straw or small hose, you can't put out much volume, for airbrushes and spray guns it takes a certain amount of volume at a certain air pressure to give you the desired results. Little compressors are like your lungs, they may be able to spray at high pressure, but not at very high volumes or air or for very long.
Reduce means to reduce/lower the viscosity/thickness of the paint or finish you are spraying through your brush or sprayer.
HVLP means High Volume Low Pressure, this refers to the requirements of a certain class of spray guns.
Gravity Feed means that the forces of gravity are used to push the paint into the path of the air that will spray/atomize it.
Siphon Feed means that an airbrush or sprayer uses a siphoning action to pull paint from a reservoir that is mounted below the body of the airbrush or sprayer.
Side Feed refers to airbrushes or sprayers that have a side mounted reservoir, they can be gravity fed, siphon fed, or, with the addition of a pressure pot, pressure fed. This means that the paint is pushed into the airbrush or sprayer under pressure, this requires less air pressure for the airbrush or sprayer itself, and because of that less overspray. Be warned though that this also means that you have to have an air hose or propellent hose hooked up to the pressure pot too.
Atomize means to spray or turn a liquid into a mist by mixing and propelling it with compressed air or a compressed gas such as CO2
CO2 is Carbon Dioxide, the same gas used to carbonate your favorite soda or beer.
Backflush is a term used for using an airbrush's normal flow of air to push paint and debris back out of the fluid nozzle and paint channel area by blocking the needle cap of an airbrush while compressing and retracting the airbrush's trigger. Because the air is blocked from going out the front like it normally would it is forced back through the fluid nozzle and paint channel and into the fluid reservoir. Backflushing is also referred to as "Boiling" because of the roiling of the fluid in the reservoir resembling boiling water.