1. Offer a spot: If you have your own parking spot, you can 1) recoup some money by renting it out per-hour (you set the price and the hours it's available) and CARMAnation takes 15%, 2) rent out your spot and decide to donate proceeds to charity (awwww), or 3) you can list it for free because you are a saint. Literally, pretty sure the Pope is on board.
2. Book a spot: You search for a parking spot by address and can look within a five-mile, two-mile, one-mile, or four-block radius (basically, if you're bringing a bike, you'll have way more free parking options), and it'll furnish you with all the available parking spots in the area. The prices range from around $6 an-hour to free to 99-cents (someone has one right now in SOMA for $0.42 an hour), and all of them come with a full rundown of the spot -- i.e. is it in a private garage? What size car can fit in it? etc. Once you've found a spot, you book it for however long you want (/it's available), and BOOM (possibly) free parking.