In this case I painted my driver's side fender.
List of materials:
1. Paint Gun (I used a $15 gravity feed gun from Harbor Freight, as far as I'm concerned it worked flawlessly, but I haven't used it again, so I don't know about durability)
2. Paint (I went to my local body shop supply place and had them match a quart of acrylic paint to the color of my car, it cost about $29 plus tax)
3. Clear coat (I used a aerosol clear coat, because it was cheap ($20) and I wasn't sure if I was going to mess it up or not. You can also get a can of clear coat and run it through the gun, which is more expensive, but probably better if you are painting a whole car. If you get the aerosol stuff, make sure it has a variable fan tip, not a round tip.)
4. 320-400 grit sandpaper (I used a 320 grit sanding sponge from autozone, it costs about $6.)
5. Denatured alcohol (I don't know how much this costs, I found some in my folks garage.)
6. Tack wipes ( I think this is what they are called, they are wipes you buy at the paint store, $2.50, and they pick up all the particles that may have been left behind by the denatured alcohol.)
First, you need to take whatever part you are trying to paint, and depending on the condition of the clear coat, sand it down suitably. From what I've read/been told, if the clear coat is in good condition, you can simply "scuff" the clear coat with 320-400 grit sandpaper, which is what I ended up doing. If the clear coat (or the paint itself) is in bad shape, you will probably need to sand it down to create a smooth surface for the paint, and possibly apply some primer, and sand the primer.
My clear coat was in good shape, so I ran over it with a 320 grit sanding sponge, no water, but you can wet sand if you so desire. I really don't know the benefits of wet sanding, anyone with insight feel free to chime in.
This is what my fender ended up looking like after I sanded it.

Make sure you get into all the crevices, and pay special attention to the edges of whatever you are sanding, as the edges will chip more easily than the flat surfaces.
Next, you will need to wipe down the surface to remove all the dust and anything else that would be detrimental to your paint. I used this denatured alcohol and a paper towel.
After that I used the tack wipes, which I neglected to take a picture of, to remove anything else that may be left behind.
After that, you need to secure your item for painting. Some people use a paint booth, but I just took some string and hung the fender from some trees. Make sure that you cover up anything you don't want paint on, because overspray is necessary for you to do this right.
Here is a picture of the paint gun I used:

This is a picture after the first coat of paint.
When you are painting, there are a couple of things to take into consideration:
First, you want to make sure that you don't "fan" the gun. By that, I mean that you have to hold the gun the same distance from the surface all the way across, usually 6-8 inches. I had trouble with this, as I was wanting to kind of arc my arm, causing it to be farther away from the surface at the edges, and closer in the middle, if that makes sense.
Second, you want to make sure you start applying paint before you get to the first edge, and "follow through" on the other side. If you painting from left to right, start spraying paint before the edge on the left, and continue after you get past the edge on the right.
Third, overlap 1/3 or 1/2 of what you previously sprayed. If you are painting from top to bottom, you'll want to go over about 1/2 - 1/3 of what you painted first.
I allowed about 15-20 minutes between coats, but the guy at the paint store said "Alot of people come in here talking about coats. It's more about coverage." So basically you want to make uniform, even coverage, let it dry a bit so that it's not tacky/sticky to the touch, and then apply another coat. A good trick for determining when it's not sticky is to place a piece of tape on some part of what you're painting, in this case I used one of the mounting brackets on the fender, because no one will be able to see it.
Here's the second coat:
and the third:
Once you allow those to dry, it's time to do the clear coat. This is the aerosol clear coat I used. Like I said, it may be better to buy a can and run it through the gun, but once you open it and it comes in contact with oxygen you have to use it in a day or so. So if you only need to paint a little bit, the aerosol can works well.
And here's the finished product:
Take my word for it when I say wait atleast a day before you try to install whatever you've painted. My impatient dumbass tryed to put the fender on after letting it dry about 2 hours, it was dry to the touch, but when i was putting it on the car my thumb sat in the same place while I was tightening some bolts, and it left a thumbprint in the clear coat. I was super pissed, but I guess you could call it a super-custom job.
Anyway, if someone has anything to add or refute, feel free to post up. All and all I'm happy with the outcome. Price wise, I had a shop quote me $110 to paint the fender, which would have come out to a total of $140 including the fender itself. I could have driven a few hours and picked up a fender that was the same color for $65, + about $30 in gas = $95.
The grand total of this project ended up being around $100, and I picked up some knowledge, so I'm happy.