We often get asked "so, how do you build a boat dock anyways." This video is the quickest explanation, built primarily by children at a summer camp. All you need is dock floats, treated lumber, basic hardware and tools.
As you can see in the video, build a "box" frame using 2x6's. Then attach the float drums underneath using a 3" Lag Bolt and 2" Fender to hold the floats in place. Flip the dock over and attach your decking, which can be treated lumber, composite wood or plastic grated panels. Add your dock cleats, ladders and accessories and you're done!