The directory layout (referred to sometimes as the filesystem or filesystem layout) in linux is one of the "tree" style. / is the base directory, from there comes everything else. /home is the home directory, it's located within the / (root) directory at home, so it's shown as /home Same with boot, it's within / so it's shown as /boot and so on. There are quite a few threads that describe this better, and how-tos written as well, I'm just giving you the tip of the ice-burg to help you understand the need for things.
You only NEED a / everything else will be created within that. For now, only create what you NEED, later you can change things.