Permissions Groups allow you to add extra permissions to normal users, without them having access to the system settings. You can give users permissions to create things like blog posts, knowledge items and new polls.
The first step is to set up your Permission Groups. You can configure each group to give offer different sets of permissions. You might call a group 'Blog Editors' and another 'Knowledge Publishers' and attach the appropriate permissions to each.
The video below explains this process in full.