What does an orgasm feel like?

My boyfriend of almost two months and I have recently started fooling around. He Knows I've never orgasmed and he wants desperately for me to orgasm and that he is the one to help me do it. He has eaten me out/fingered me/rubbed my clit for the past three times we've hung out and i still haven't orgasmed. He always asks me if I'm about to, but I have no idea ?? Everything he does makes me feel wonderful and he does it for a long time, but I still haven't orgasmed. I just want to know what to tell him when he asks if I'm about orgasm. Like what does it feel like to the moment leading up to it and what does an orgasm feel like?