Community hosts can appoint moderators. A moderator is a person who help moderating the community. Typical tasks that a moderator perform are helping new members find their way around the community, answer questions and help maintaining the order in discussions.
To find the moderators of a community, open “About” in the menu above and scroll down below the community presentation. If you want to contact any of them, just tap or click on their avatars and follow the link “Send message” in the menu on the left.
Some communities may not have moderators. Then the hosts handles all moderator tasks themselves.