I suck at grinding

So like the title says, I suck at grinding. Or moving my hips around at all, really.
My BF and I are both virgins and plan to remain that way (hopefully until we're married but I definitely wanna wait until after I graduate) but we still like to get down to it. I have tried grinding on his crotch with underwear on but the fabric just rubbed and created a painful friction for him, so I haven't done anything in fear of hurting him. The other night though he was laying down, I was above him and giving him a hand job/head while he fingered me. We were kind of in the 69 position but not really. Anyways he asked me to basically grind on his finger; I'm not sure why, he seemed pretty horny that night, and I told him I didn't know how to. Thank goodness we're super comfortable with each other, otherwise that would've been embarrassing. 
So how do I grind on him (or his fingers. Is that even a thing??) without hurting him? Neither of us are willing to come into contact with each other in THAT region just to be safe, so some clothing has to be involved. Thanks guys!