when the guy wants to try things from behind (his behind)

Last year my SO and I had drunk sex I fingered him, he enjoyed it a lot. It was weird as it can be, but we were super drunk. One day I passed by an adult store and got a little dildo to play some more with him. We haven't used it in a while, but two days ago we were talking about things we would like to do in bed and he suggested a strap on. I've watched videos but I don't know what to think lol any ideas?