What does it mean when a guy tells you he’s submissive?what do you do to him?

My bf of one year told me a few days ago he’s a sub, after apparently pretending he’s a dom for all this time, saying he doesn’t really like it and would like if I dominated him more. I’m not like that at all and I don’t even know what that’s means. I’m not comfortable being dominant and it makes me feel weird because a guy dominating me is always such a turn on and now he’s telling me he wants me to be dominant to him from now on and I just ..🤦🏽‍♀️🤦🏽‍♀️ kill me.