The conversations or threads in your group are displayed in order, based on the time of the last response.
i.e. a conversation started three months ago, but with a response posted in the last five minutes will be displayed at the top of the screen.
It is also possible for hosts and moderators to pin up to five threads. These will always be displayed at the top of the screen, before the general discussion, but their order will also change based on when the last response was posted.
Guild displays the photos of the first and last contributor next to each conversation. If only one photo appears there may not have been any responses, or the person who started the conversation is also the last person to contribute.