A Clipper Card is a transit card valid on most transit services in San Jose and the greater Bay Area. It works on VTA, Caltrain, bart, and other local transit agencies, including San Francisco's Muni.
The card itself costs $3 and works using RFID technology. Cards may be purchased and fare added at any Walgreens store. Fare may also be added using the ticket machine at any VTA light rail station.
You can choose to add "Clipper Cash" for general use, or you can add stuff like monthly passes for certain transit agencies.
Paying with Clipper on Caltrain gives you a $0.25 discount off each ride. Remember to "tag on" (scan your card) on the platform before you board the train, and to "tag off" when you reach your destination.
To ride VTA buses, tag on once onboard.
To ride VTA light rail, tag your card before you board. There is no need to tag off, because all rides are a flat $2 fee.
You must have a minimum balance to begin a ride, but the card will allow a negative balance, which you must pay when you recharge.
You can also set up your account to automatically reload fare or passes.