Now comes the fun stuff! So now you've got all the layers laid up on your project, and it's time to finish it off.
The first step is to sand down any rough/high areas of fiberglass. You can do this by hand, but by far the easiest method is a DA sander with about a 100-120 grit paper on it. You don't have to have it sanded down 100% smooth, that's where the fillers come in.
Once you have the project rough-sanded, it's now time for fillers. I personally use what has come to be called a milkshake for the first layer of filler, and then finish off with some simple fillers, just like you would doing body work.