Do a search on "bedding" and check out Chad Dixon's (Nesika Chad) work. You will not find any better info and pictures on the net about bedding than right here. The article that GNERGY linked is also very good. Floating a barrel is very easy. I start with 40 grit sandpaper wrapped around a dowel for removing material. Here are some pics of a barrel I recently floated.
If you are going to float and bed, I would recommend floating before you bed, but be careful not to take too much material out, because when you bed, it may very slightly raise your action and barrel. Keep checking fit regularly during the process so your removing in the right spots. I used a dowel (drill bit in this case) to get an even and level bottom and hand used the sandpaper for the top of the sides. Once the action is bedded, come back and finish up with a finer grit paper. 100 is what I use, then put a few good coats of oil down to help seal it up. It won't completely seal it, but it helps, IMO.
If the experts have anything to add or change, please do.