As simpak eluded, it's like a lecture. You can think of it as practically being a lecture. Sometimes, they use this to fill in content when they have fallen behind throughout the course. They can even sometimes make ones which were not originally scheduled. Depending on how behind they get.
Most of the time however it involves the lecturer going through a number of questions:
1. Questions that have been made for the workshop.
2. Questions that students have sent in or ask during the lecture.
They will ask a member of the audience to suggest an answer (as they do in some lectures anyway). Because they are really similar to lectures, they are optional, they're recorded, and you'll be in a lecture hall. So it's not that similar to the first year biology workshops.
Many people asking about the tutorials and practicals etc and how they are run months before the course starts. Lots will be out of context and not be clear until you actually start. You get a whole lecture on it on the first day, access to information online, emails, alongside reiterations throughout the semester. This course is wonderfully co-ordinated, one of the best subjects I have been in. It is very transparent, organised and efficient.