Within Guild, it's easy to see what needs your attention as it will be marked with a pink dot.
In the list of groups you're a part of, the number in the pink dot next to each group listed indicates the number of conversations with unread messages.
In a group home screen, the number in the pink dot next to each conversation title indicates the number of unread messages in that conversation.
Tapping a conversation will take you to the first unread message (so if you've already read a few messages in a long conversation there's no need to scroll to find new content). Your first unread message will be marked with an icon of a paid of reading glasses.