It’s hard to remember, but I’m pretty sure I first learned about mahjong (not mahjong solitaire) in the same way I’ve learned about most things in my life, Japanese cartoons. It looked interesting so when I saw a mahjong set for sale at a Half Price Books years ago I went ahead and bought it, got a book on mahjong, and never learned how to play. I didn’t know anyone who played and the mahjong software selection is bad enough now and was even worse then.
My interest was rekindled a few months ago after playing gin rummy for a while and one of my Twitter friends mentioned that he’d learned the basics of mahjong by thinking of it as essentially a rummy game. After all, the premise is that you’re forming tiles into sets, either sequences (e.g., 1-2-3 of the same suit) or three or four of a kind to form a winning hand. I re-read my book, managed to find a decent mahjong iOS app to practice with, and even found a group in my area to play with IRL.