From Online Manual
The Core Features page of the Administration Center is where forum administrators can enable or disable certain features with SMF. Once you have enabled or disabled any core features, you must click save for the changes to take effect.
The Calendar feature of SMF can be used to show forum events, holidays, and user birthdays.
Advanced Profile Fields
This feature can be used to hide standard profile fields, or add new ones. The administrators can also choose whether or not certain profile fields show up at the registration screen.
Karma is SMF's reputation system. Users choose how popular members are. Settings for karma can be found in Features and Options after the feature has been activated, while permission to change other people's karma can be granted to users in General Permissions
Moderation, Administration, and User Logs
This feature logs all actions taken as a moderator or administrator. This also allows moderators and administrators look at any actions that a user has done in their profile.
If this feature is enabled, moderators can choose boards in which all posts need to be approved, which membergroups need to have their posts moderated, and more. Once this is enabled, the administrator may set permissions at Administration Center > Permissions > Post Moderation.
This feature allows users to pay to change their membergroup, get more access, and more.
If this feature has been enabled, administrators may generate reports as to how the forum is set up, what features are enabled, and more.
With this feature, administrators and moderators can issue warnings to members if they have broken forum rules. As the warning level increases, the user's permissions decrease.
Search Engine Tracking
When this feature is enabled, forum administrators can track search engines when they look over your forum.