Start at a gym:

“Climbing gyms are accessible, relatively inexpensive, and all you need is a pair of rental shoes. Gyms are a friendly, welcoming place, especially for a sport that can feel very intimidating. If you all you see is Alex Honnold free-soloing El Cap, the sport looks terrifying, but literally, anyone can go to a climbing gym and get started.” San Francisco climbing gyms like Planet Granite and Mission Cliffs offer classes on everything from how to belay to how to lead-climb.