There are a variety of roles, that allow the user to do different things. By default, each higher level can do everything the previous level can do, plus the listed information.
Are allowed to read content, even if is set to private. Can leave comments if “User must be signed in” setting is enabled.
Are allowed to write posts, however they cannot publish them. The posts must be published by someone else. They can edit a post they created until it is published.
Authors are allowed to write posts, and can edit and publish their own posts.
Editors can edit the posts of other people. They can also publish posts that are not published yet, regardless of who created the post originally.
Admins can change settings within WordPress. This includes all configuration settings including: themes, menus, etc.