tbol, for documentation of the sculpt brush, and the retopo feature, you can check the documentation in the release notes for recent versions, or check the blender wiki. Basically, to use the sculpt function, the controls of which are located in edit buttons, you go into sculpt mode, from the selection menu on the main header, same as going into weight paint mode, and vertex paint mode. then you can, provided your mesh is high poly enough ( and that’s why you use the multires feature ) treat you mesh more or less like clay, and paint in features, or chip away, or inflate, or whatever, depending on the type of brush you have selected. but that leaves you with a very dense, high poly mesh, which is not always practical, so, you use the retopo feature, which allows you to use the surface of any model, as a guide, over which, you can create a new mesh, that conforms to the surface of the guide mesh. they are features worth looking learning, so check here for tutorials, i know there is one on the retopo feature in the tutorials section, and check the main site for release notes, and documentation, and also the blender wiki. Of course, these things don’t replace basic modelling skills, but it looks like you have some of those already.