Same as in your other topic about Blender texturing...we need more information.  I think a Google search would get you basic results as far as how the software works, and the details about how well it would work for your specific project will depend on us getting more information about said project.

I've used it before. It's pretty nice for building the base mesh, but depending on the requirements of your game you might need to use the base mesh as a sculpting base to obtain a more detailed high-poly, then bake some details back to the base mesh. You'll probably also need to put some effort into making clothes; there are some publicly available clothes, but they tend to be fairly low quality, and somewhat generic. The clothes make the man, so unless you're making a game featuring loincloth-clad cavemen, you'll probably spend more time modeling clothes than you will modeling people.