I don't know exactly, but my guess is that they reproduce the same way worms do. Worms are hermaphrodites, meaning they have both male and female reproductive organs, and due to this, they link together like this (diagram below) and the gametes from one worm goes to the seminal receptacles of the other worm, thus reproducing the species.
Because snakes have the same kind of make up as a worm, I would assume this is how they would reproduce as well.
または あなた could just Google it and not listen to me at all. Your choice.
EDIT: Yeah, I don't know what I'm talking about. At least I know how worms work though. xDD
Well, firstly, they have to find another snake that likes the same things. Fine dining, midnight slithers, watching the city lights, romantic 映画 ect...
Then after a while, when they're both ready, they'll fall into eachother and make love.