Tours are normally conducted by volunteer students. Sometimes the admission directors will introduce themselves to the visitor group and hold a brief introductory session then hand off to the student tour guides to walk the campus with you. At some schools the admissions officers may hold a more in-depth session in a lecture hall setting after the tour has ended - they are all slightly different.
Some hints to help you get the most out of your tour experience:
1. Check online to see when official tours are being given and make an appointment.
2. If visiting multiple schools in one day; don't try to do more than two each day. Allow extra time, as tours and informational sessions frequently run late. Plot driving routes and book hotels in advance.
3. Wear good walking shoes.
4. The student should register at the admissions office. Schools do keep track of all contacts with applicants. In a recent survey, 46% of schools said campus visits have a POSITIVE influence on the admissions office.
5. For parents: let your student ask questions of the tour guide.
6. Eat lunch in the school cafeteria. Do you like the food selection?
7. Pick up a student newspaper.
8. Sit in on a class. This must be arranged in advance through the admissions office. Sometimes it must be arranged through a department head, but schools really do encourage "student for a day" programs.
9. If possible, students should arrange to meet an admissions officer.
10. If you meet an admissions officer, send a thank you note immediately upon returning home.
11. Prior to the visit, make a list of questions you want to find answers to. Don't ask questions of the admissions officer that you can easily get answers to on the school's website.
12. If possible, parents and students should try to take different tours of the same school, if 2 separate tours are leaving around the same time. You'll get two different perspectives which you can talk about later over dinner.
Have fun on the tour, imagine yourself studying there and being a part of that campus. Jot down your thoughts and impressions about each school while everything is fresh in your mind; keep all your notes in one place so you can review them when you are getting ready to make your final "apply list".
Here are some quick links of tour and info pages for various schools.

University of California, UC system click here
University of Michigan, click here
A link to my own campus tour videos, click here