I don't know what to do with my hands during sex

My bf and I have been more sexually active recently. He's experience but I'm not. He fingers me, goes down on me, goes on top of me, grinds on me. And I feel like he is doing all the work. I want to pleasure him back. I want to give him a hand job before I try a blow job but I get shy when his penis is out bc it's fucking huge. I kianda have an Idea of how to do a hanjob but I don't even know how to start. Should I ask him to guide me or would that be a turn off? Also my knees hurt af whenever I try to ride on top of him what exercises can I do to help with that? And last question how does a small girl like me adjusts to a big dick lol