are you on an Apple product? (like an iPad, or Mac?) or on a PC (laptop) that uses Microsoft? If Microsoft, you should pull up not only the list of people who you are friends that are posting, but the latest posts from the last one you clicked on previously. If you want to make a post on the groups you belong to, go to the search bar in the top left and drag down the menu or type in the page name. Once on the group page, if the page is set up to actually allow all members to post, then it will ask "what's on your mind" and a create post button. If the page is set up so that only administrators can post (which some are) then you will only be able to response to posts.
I know nothing about an Apple product other than I know it shows differently.