BART, or Bay Area Rapid Transit, is a safe, reliable and fast public transportation system in San Francisco. For over 40 years, BART has connected the San Francisco Peninsula with Oakland, Berkeley, Fremont, Walnut Creek, Dublin/Pleasanton and other cities in the East Bay.
I found BART to be a very user friendly system, as well as an inexpensive way to get around the city, but some people get confused and panicked with public transportation, imagining trying to navigate the different lines.
First, do a little homework! Look over the map and figure out where it is that you need to go and which line you need to take to get there. Also, don't be afraid to ask a friendly looking passenger for a little help if you're confused. Not all BART passengers are as cranky and aloof as they look.
In my opinion, BART fares are average as a form of public transportation. Fares are based on how far you travel. To check fares, visit the Fare Calculator. Discounted tickets are available , and kids four and under ride free. BART tickets are plastic, basically like a credit-card with magnetically encoded value. Fare gates automatically deduct trip fares from the stored fare value on ticket. It certainly is an eco friendly alternative to driving, and it'll save you a bundle on the super high gas prices and parking rates that you're going to find in the city.
I have an awesome app called HopStop, which has always been super helpful in being prepared for riding BART. The app provides directions via subway, (and bus, regional rail, walking, and/or bicycle). It also offers multiple route suggestions, schedules for hundreds of trains, and official transit maps for many cities including, but not limited to, the Bay area. You'll never get lost again!