Having a car in San Francisco is not a necessity. It might even be a nuisance and definitely an unneeded expense. The bus system is easy to master; there are maps available at the tourist office and other places around town, showing where they go. The ride costs $1.50 but only $.50 for Seniors; you are given a paper receipt torn at the hour that the ticket lapses, so you can make transfers for a couple of hours. The subway system is also easy, whether the BART or the Metro system. Along Market Street, one of the main streets in town, there are trolley cars reminiscent of earlier days; these are the same price as the buses and may be used with a transfer; they will take you from the Ferry Building to the Castro.
Everyone wants to ride the Cable Cars, at least on the first visit. The tickets these days are $5.00 for a single ride, but there is an "All Day Fare" for $11.00, so take advantage of this and ride to your heart's content!