The vast majority of automotive paint products can be divided into 2 different resin types Thermoplastic and Thermoset.
Also known as 1K (component) products. These will reflow when exposed to heat or solvent. Lacquer is a good example. If you soak a rag in lacquer thinner let sit on the fender of a factory 1957 Chevrolet paint job, you will be able to just wipe the paint right off. Also when you buff out this same 57 Chev, the heat and friction from your pad and compound will may the paint reflow for a smoother finish.
Theromplastics cure by the release of solvent, they do not use a castalyst. Because of this they have reduced durability and gloss levels. They also tend to continue to shrink for a long time. Meaning that primer sand scratches and body work may reappear later on.
Also known as 2K (componet) products. Almost all factory finishes are themoset. They cannot be reflowed by either heat or solvent.
Thermosets use a catalysing agent to help cure. This helps them cure with greater durability and gloss and have very little shrinkage during the curing process. However,because of these catalysing agents we have limited time to use them once they have been mixed, this is known as a pot life.
IMPORTANT: Thermoplastic and Thermoset products do not always mix. If the products chosen are not compatible, wrinkling or lifting can occur.
If you are working on a car and don't know which paint is on it, you can soak a rag in lacquer thinner and let it sit on the paint for 5 minutes. If it wipes away or wrinkles then it is probably Themoplastic and should all be removed. If it does not affect the finish then it is probably Thermoset and should be aresonably strong finish to start with.
There are also 2 basic styles of paints, single stage paints and basecoat clear coat paints.
Single stage paints
Sinle stage paints do not get clear coated, because of this they should only be shot in solid colors. If you shoot a metallic color, it must be perfect, because you cannot wet sand and buff it. If you try to do this you will cut the top of the metallics off and this will leave you with bad flake orientation and a very mottled and hazy look.
Basecoat clearcots paints are now used by every car manufacture, even for solid colors. Because with a nice layer of clear coat on top of the color, you can wet sand and buff out any scratches and paint imperfections. This is nice when they have any mishaps in the factory or dealerships, they do not have to repaint.