Lectures usually take place in large lecture theatres which may hold 300 students or so. You will generally find the whole year group gathered for that lecture so the size of lecture room will be determined to some extent by the size of your year group. If there are only 30 of you then you may find that a seminar room is used.
Students sit as an audience and the lecturer talks to them, usually for 50 minutes or so, perhaps with some visual aids such as overheads, video clips or Powerpoint etc.
Lecturers may ask questions and some plucky students may answer but as a rule the lecturer lectures (ie talks about the text / topic) and students listen and take notes (in an ideal world).