In CAS you'll notice your units have different classes. 

• Lecture: Large formal classes that provide overviews of unit material, run by a lecturer. Lectures are often recorded for you to re-watch later, so you can click the online option allowing you to take another class at the time of your lecture. 
• Tutorial: Also known as a "tute", this is a small group discussion led by tutors, of a unit's weekly topic. Tutorials are compulsory unless stated otherwise on the unit message on CAS, on LMS, or by your unit coordinator.
• Seminar: A class focused on a specific topic, designed to encourage your critical thinking, independent research and teamwork while allowing you to explore the subject in more detail. Seminars are compulsory unless stated otherwise on the unit message on CAS, on LMS, or by your unit coordinator.
• Lab (laboratory): A practical, hands-on environment where you conduct experiments, tests or practice skills related to your field of study. Labs are compulsory unless stated otherwise on the unit message on CAS, on LMS, or by your unit coordinator.
• Workshop: An interactive session where you engage in practical activities, discussions or exercises related to a specific topic or skill. It’s designed to provide hands-on learning and foster collaboration among participants. Workshops are compulsory unless stated otherwise on the unit message on CAS, on LMS, or by your unit coordinator.

Not every class runs every week, and there are some activities like fieldtrips which are run over a short intensive period, ask you're UC if you're unsure on which classes you need to attend.