From B2evolution

User levels (0-10) are almost completely deprecated in versions 0.9.2+.

Most of what a user can do or cannot do is controlled by the User permissions.

Starting with version 2.0, User with a higher level can be given permissions to edit posts by users of lower level, or of equal level.

In previous versions here is what user levels would allow:

• Level 1 and above:
  • Ability to view link to admin section (users with level 0 can still login into admin, but there's no good reason for that, except in rare cases, so they'll have to find out by themselves...) (on versions < 0.9.2).
  • Ability to upload images (on versions < 0.9.2).

• Level 2 and above:
  • Ability to generate static pages (on versions < 2.0 -- In 2.0 ability to generate static pages is granted to anyone with any post permission.).

• Level 5 and above:
  • Ability to edit timestamp on posts and comments.