The top of the course homepage has information welcoming students to a course by default. Once everyone has joined your class (after 12 week starts for most course, after 14 week starts for AP), you can change the bulletin board. You can make this interactive (with clickable links) or display a static item. You can change this as often or as little as you like as long as you change it from the default at least once.
Some teachers put a monthly calendar with important dates (this is especially helpful towards the end of the semester when students have multiple due dates, final exams, etc. to keep track of).
Some teachers put information about review resources - shmoop, USATestPrep in this area.
I create a set of "buttons" and attach them to my course resource newsletters for each module so the students can access them easily. I've attached pictures of the "buttons" I use. Basically, I just attach the link to the newsletter to the image. I can provide a video if you decide to go this route.
This space is pretty customizable and you can often find creative things other people have made for their bulletin board on Yammer!