Blowjob

My boyfriend wants me to go down on him. I'm not comfortable with that just because I don't really know what to do. He's very respectful of me and doesn't get upset at all when I don't. He always tells me it's not a big deal that I don't because I don't have to do anything I don't want to. But I kind of want to because I know he wants me to. I don't know how to do it