Shed floors are usually built like the picture below and primarily consist of band boards, rim joists, floor joists, and skids. There are any number of ways to anchor your structure to the ground, the 2 most common being with posts in concrete that are attached to the floor itself, and the other by cable tie downs.
If you check with your local county building inspector, they can let you know which method they require. Nine times out of ten, I end up using the posts and concrete method, sometimes 1 anchor in each corner, sometimes just caddy corner - or only 2.
Band Board - There are 2 of these. If your outside dimensions are 12x16 for example, the longest board will be the band board, and in this example, would be the 16' length. All joists and rim joists are attached to the band boards.
Rim Joist - There are also 2 of these. They are the same length as all the joists, however they are the outer joists, hence the term 'rim' joist.
Joists - Joists are the cross members and are running perpindicular to the band boards. Typically they will rest on 4x4 skids.
Skids - Skids are the primary supports and depending on the size of your shed can range anywhere in size from 4x4 to 6x6. I very rarely used the 6x6 size, so 4x4 is pretty common for the types of sheds that are built with my shed plans.
Sheeting - Sheeting is the flooring or planking. It can be 4'x8' sheets that are 5/8" thick or 3/4" thick. Sheeting can also be accomplished by laying down rows of 2x4s, 2x6's, 1x's, or 5/4" deck boards. There is no wrong or right and is your preference.