Cranky has an airbrush tutorial on YouTube, real good. Basically, the long needle, the trigger button (which becomes free when the needle is removed), the tip... real basic. See the Doc's vid to see how few parts there are. Gently wipe that needle clean with a towel soaked in thinner, put it back together. Before disassembly, squirt lacquer thinner through (we would spray into the paper towel for severel seconds, then push the tip tight into the towel tight while still spraying; forces thinner to back up- WEAR EYE AND SKIN PROTECTION!). Clean out the bottle; add another dab of thinner; and repeat the "spray-thru" procedure. Have a container such as a metal coffee can (do they still have those?) to dispose of waste thinner.
TIP- ask a body shop if they have any leftover empty 1 or 5 gallon metal thinner / reducer cans. I use a 5 gallon with a metal funnel, topped with window screen so nothing else goes down into the toxic abyss.