Well, at first, with foot power! That's always an option, even for us old folks! And boy did we walk and walk and walk and walk!!!!!
As we got more acquainted with the city, we also took the bus, streetcar, and cable car.
Another option we took advantage of was the Citysightseeing tour buses. For one price, you get to hop on/hop off where ever they have stops--boy, did we love this option!
We rode around the whole route first, just to get the hang of where it goes. Then we decided where we wanted to hop off. Here's Zip--hoping off the bus!