Why do members join my group without me getting any member applications?

A group can have two different settings concerning the new entrant of members:

1. New members will be approved by the Group Manager
2. Everybody can join the group

With #1 the Group Manager has to approve every single member, who wants to joint the group.
With #2 every new group member can join the group by click, without being approved.

If you want to change that, please click as Group Manager in your group, click the tab Settings and change the selection box New Members.