Although many people are afraid of spiders, virtually all the spider species found in San Mateo County are harmless to humans. Unlike mosquitoes, which seek out and feed on people, spiders have no interest in biting us, and will only do so in self-defense.
Spiders that find their way indoors can be gently relocated outside (you can scoop them up using a piece of cardboard and a container, or vacuum them up and empty the canister outside), or squashed if you prefer. Sealing up cracks and other entrances to your home will keep spiders, as well as other pests, from coming inside.
In most cases, spiders found outdoors can simply be left alone. If you feel like there are too many spiders around your home, you can clear vegetation and debris where they may be hiding, and sweep away any remaining webs with a broom.