There are four roles: Administrator, Editor, Author, and Contributor.
An administrator can do everything. Complete power over posts/pages, comments, settings, theme choice, import, users – the whole shebang. Nothing is off-limits, including deleting the entire blog.
An editor can publish, edit, and delete any posts/pages, moderate comments, manage categories, manage tags, manage links and upload files.
An author can edit, publish and delete their posts and they can upload files.
A contributor can edit their posts but cannot publish.