Your first stop for help in a particular class should be your professor's office hours, TA, or other course-specific resources (the syllabus is a great place to start!) However, there are many 5C resources available to supplement your instructor's support.
DNS Peer Education for General Chemistry and Organic Chemistry
Physics After Dark
"PAD" runs 7-9pm Sunday through Thursday evenings, usually in E180. Its central aim is to provide free tutoring/mentoring for students taking intro Physics 30/31 and Physics 33/34 (though, depending on the individual tutors, sometimes they might assist with other physics courses)
Scripps Writing Center