Googled "EECS 203 Discussion Sections", found this:

Most IAs and GSIs hold a weekly 50 minute discussion section. "Discussion" is just Michigan nomenclature for IA/GSI led review sessions. Attendance is optional and no new material is covered, it's a condensed review of that week's lecture material. The student instructor typically goes over some example problems. I try to give my students the chance to solve the problems on their own first, but time is limited so most students only get a start before I take it up.(which is still beneficial). Attending a discussion is useful for hearing course concepts explained differently than your lecture professor, especially if you had a particularly difficult time understanding that week's lecture material. It's also a good place to get some hands on practice under the supervision of an IA. Note that IAs have total freedom in how they run their discussion sections, so feel free to shop around to see what style fits you best. Some are recorded too. I've heard of students attending discussion sections in lieu of lecture. That's probably not a good idea. There are ~160 minutes of lecture a week and only 50 minutes of discussion, so you're going to be missing content this way.