It's a bit of a trek. How much of your day do you want to dedicate to the trip? I would expect the journey from San Francisco to take 4 hours total at a minimum, more if you also explore downtown Palo Alto (which is probably worth it and adds an hour to your trip).

It's relatively "easy" to get there: You would have to take Muni line 30 or 45 from Union Square to 4th & Townsend, walk across the street, and take Caltrain. To save time, you should try to catch the Baby Bullet or Limited train, as the local train is kind of slow. Be sure to catch a train that stops at the Palo Alto station.

Once at the Palo Alto station, you can take Stanford's free Marguerite Shuttle buses to various points on campus, or you can go for a walk.

More info:

http://www.sfmta.com/30 and http://www.sfmta.com/45

http://www.caltrain.com

…stanford.edu/marguerite/MargueriteShuttle.s…

You didn't say whether you're driving or taking transit -- if you have a rental car, the drive is about 45 minutes each way. Take Hwy 280 south to Sand Hill Road. Beautiful, scenic drive. Maybe divert back through Half Moon Bay/Montara on the way North to see some coastline.

The free Stanford shuttles run frequently during weekdays/workdays during the school year. The service on weekends is much more limited.

A schedule is posted at the stop on the oval by the Palo Alto Caltrain station.

In addition to the Stanford Bookstore on campus, there is a Stanford store in the Stanford shopping center.