You can interact with a group via posting Activity or starting a new Discussion topic. But which should you use?
The Activity Feed shows everything that is happening in the group (including new topics and replies), but you can also share activity here.
In general, Activity Feed posts get pushed down by other Activity Feed items and should be something timely like sharing a news article, YouTube video, or short comment (up to 3 lines) that doesn’t necessarily require a reply. It will be seen by those looking at the group now (or soon after posting), but may be missed by others viewing later. Think of it as a post on Instagram or Twitter.
Discussions are for more in-depth interactions between users. If you want to share your in-depth review of a location or experience, or if you want to gather information by asking a question like “how do I use the subway in New York in a power wheelchair?” – discussion topics are the best way to do it. These last forever and can be found via searching by other users.
(Note: Not all groups have discussion forums. For example, group for sharing vacation pictures is more suited to having only an activity feed.)