Seminars are for small groups of students studying the same course. They are normally led by a tutor in a seminar room.
Seminars are designed for students to talk about topics in the course reading or lectures in detail, so students have to take an active part in the debate. Sometimes the tutor will lead the seminar, or they might choose students to make a presentation. But whether you’re presenting or not, you’ll still need to do some work before and after the seminar to make the most out of them.