I would like to sculpt but I don't know that shapes I can use to sculpt with. I know that the shape I'm sculpting with needs a lot of vertices to sculpt good, but I don't know all shapes to sculpt with.
You can use any shape you want.
Sculpting modifies a mesh in real time, so at any point you can switch to edit mode and edit the polygons directly, then switch back to sculpt mode, etc.
There are two usual workflows for sculpting:
You don't need to subdivide your mesh if you use dynamic topology, the mesh will be dynamically subdivided as you sculpt.
Enable it in 3D view > tool shelf > Dyntopo (Topology pre 2.71), or by pressing CtrlD:
This will create a mesh of triangles, so depending on the project you may need to do retopology after you are finished sculpting.
Non-destructively subdivide your mesh with a multi resolution modifier, which lets you handle multiple levels of subdivision at once.
Because of this, it's quite useful to use on a low poly model, sculpt details, and bake normals.