Imma back :P (have been very slowly working on the guitar over the last couple of months)

Start wet sanding at about 1000 grit wet and dry paper, then work up to 1200 then 2000. If your local hardware store doesn't carry these finer grades; an auto accessory store will have them.

This is what my manual says. Pardon my ignorance - when I use wet and dry sandpaper, what is the "wet" part and how does that work?