Cornell University provides access to many top-notch professors. Some professors are more focused on their research than on their students, but it varies considerably from college to college, and department to department. All professors are highly qualified and are experts in their respective fields of study, but not all are heavily invested in their students. TAs provide more hands-on, individual teaching and are generally very knowledgeable in their field, but not all are as proficient as professors.
Overall, it is up to the student to take the initiative to visit professors and TAs in office hours. Professors and TAs are happy to explain material in-depth, but getting their attention can be difficult in larger courses and majors. Cornell is notorious for its intense workload. Most professors are unsympathetic, and while willing to accommodate personal needs, they make sure their students are kept very busy. If you go to Cornell, be willing to work hard, weekdays and weekends.