I started by crewing for somebody who was just getting started in SCCA racing. Met him at a BMW Club Ice Raing event (really an autocross on a frozen lake, and also the first "competitive" driving event I did) and he was one of the fastest drivers out there - in a Chevette on bald snow tires. He showed up at the next event in a caged MR2 on race tires - back in the days when a Showroom Stock race car was really showroom stock-ish, and could be registered for the street. I felt bad for him just doing pirouettes on course (mid-engine+R comps are not the hot set-up for ice), so I let him co-drive my VW Golf GT on snow tires and he beat me by multiple seconds. We got to chatting, and I ended up crewing for him at his first race school, and for several years to follow. Met a bunch of people, learned the "process" of racing, and learned about other clubs that did HPDEs and time trials.
Eventually I put my own car together for SCCA Improved Touring, got a competition license, and my bank account has never been the same :-)