San Francisco has 3 accessible airports: San Francisco International Airport (SFO), Oakland International Airport (OAK), and San Jose International Airport (SJC). SFO and Oakland are the closest and easiest to get into the city, but it could be more cost effective to look at flights into Oakland and San Jose (although this one is the furthest/most expensive with about an additional hour and half of drive time into the city).
A taxi from SFO into the city will cost about $50 and take about 30 minutes depending on where you are heading. If you wish to take the BART (Bay Area Rapid Transit--San Francisco's public transit system), you can take it directly downtown, which will take about 30 minutes and cost less that $9. Trains leave pretty frequently out of the airport too. The airport also has access to buses and shuttles into the city if you want that alternative.
A taxi from Oakland into the city will cost about $70 and take 30-40 minutes depending on where you are heading. You can take the BART from Oakland as well and it will also cost less than $9. A taxi into San Francisco from San Jose can cost almost $150+, which makes this the most expensive way to get from one of the accessible airports (unless you rent a car).
Cabs are not too difficult to find downtown, but the taxi service is notorious for being subpar compared to other large cities. There are also car shares like Uber that are plentiful (Uber was born here!).
San Francisco is known for being pretty easy to get around; after all, it is only 47 square miles! The public transit systems include the Muni (light-rail vehicles), BART, cable cars, and trains. All of them are extremely easy to use and very helpful to get to all of the major locations/landmarks. BART fares start around $1.85 and the ticket price is based on miles traveled. You can buy public transit adult passes for $2.25, 1-day passes for $17, 3-day passes for $26, or 7-day passes for $35.
Walk! San Francisco isn't that big of a city, so it is completely manageable to walk around and see a lot.
Boats are available for getting to surrounding areas like Sausalito and Tiburon, each costing about $11 one-way. There are other parts around the San Francisco piers that you can catch boats to other areas of Greater San Francisco.
