What are member roles?

When you create a group, you will be asked to set member roles. These determine the status of your group members and their ability to post and comment on the group blog.

Administrators have access to all the administration features; editors can publish posts, manage posts, and manage others’ posts; authors can publish and manage their own posts; contributors can write and manage, but not publish, their posts; subscribers can read comments, make comments, and receive newsletters.

You must have at least one administrator, but the remaining roles are not required, and there is no limit on the number of people who can occupy each role.

These are covered in more detail here.