You're automatically set as a Moderator to Topics that you create.
For already existing ones, you can request to become one by using the "Become a Moderator" button, present on all topics you follow. Once you select it, a request to the current Moderators will be sent. They have the power of accepting or denying your request. Be sure to get to know the communities first, you have a higher chance of being accepted if you are already part of it ;)
