The first step in implementing Organic Groups is to create an entity that will serve as the group type. Typically this is done by creating an entity that is a content type.

[This may initially seem confusing because we are creating a group based on a content type and groups usually contain other entities that are also content types. However, content types provide much of the functionality that groups require and the reasons for this will become more clear the more you use Organic Groups.]

Navigate to /admin/structure/types/add and give the new content type a name and description. It is usually convenient to set defaults so that: groups are not promoted to the front page; author and date information is not displayed; and comments are closed. The option of most importance is under the Organic Groups tab where the Group checkbox should be selected.

Save the group content type and return to the content types page.

If you go the Manage Fields tab for the group type you will see a new field labelled Group with a Boolean field type. (If you don't see it, make sure the OG UI module is enabled.) This field is used when users subscribe/join a group. Other fields can be added to group entities to control the permissions for the group and the visibility of the group.