Manual:$wgAutopromote

Details
This array contains criteria of automatic promotion. The syntax is: cond here may be:
 * A single condition
 * A set of conditions

Possible conditions
Possible conditions (defined in Defines.php; extensions may add more through the AutopromoteCondition hook):

Conditions with and without arguments
Each condition can be written in two forms:

Set of conditions
Sets of conditions have the following syntax: There are 4 operands available: The sets of conditions are evaluated recursively, so you can use nested sets of conditions linked by operands.
 * & (AND) — promote if user matches all conditions
 * | (OR) — promote if user matches any condition
 * ^ (XOR) — promote if user matches only one of two conditions
 * ! (NOT) &mdash; promote if user matches no conditions.

Caveats
Autopromotion doesn't actually add users to a group; MediaWiki will check whether a user meets the conditions for autopromotion whenever it checks the user's rights or effective groups. This means that a user will only appear to be in a group on Special:ListUsers if they were added to it through Special:UserRights. It also means you can't directly remove a user from an autopromotion group through Special:UserRights: $wgRevokePermissions might be useful for you, or if you're not using MediaWiki 1.16+, a workaround is available.

Example
If you wanted to autopromote each user to captain upon his having both confirmed his email address and either made at least 100 edits or registered his account at least 60 seconds ago, you would use: