The job of a teaching assistant is not an easy one. Some departments invest more than others in developing the teaching skills of their TAs. Some universities do more than others in this regard. To get the most out of your situation, consult with experienced TAs on your campus, and learn exactly what is expected of you. Lectures, Seminars, etc.
Lectures are the primary form of undergraduate instruction in U.S. institutions.
Lecture courses may enroll as many as 500 students or be as small as 20 or 30 students. Although attendance may not be recorded, you are nevertheless expected to attend. Material covered in a lecture class may be closely related to the reading assignments or may be completely new material. Doing the reading before attending class is a sure way to improve your comprehension of the lecture. You might wish to record lectures on tape, especially if you are having trouble following spoken English in your first weeks of school.