In the mobile app, a message board post's menu has Report post, and each comment has Report. In Chat, tapping someone else's message offers Report message. Choose a reason and the report goes to Magpie for review; content that breaks the Acceptable Use Policy is removed.
Block hides a person's posts, comments and chat messages from you, and they are not told. Blocked people are listed under Account settings, where each can be unblocked.
The Terms of Service and Acceptable Use Policy now say that objectionable content is not allowed and describe how reports are handled.