How do you even ride on top? I'm so lost. 😓

Look, I love sex. But I was a virgin when I met my husband. Never did a dang thing. He's my first everything. There was ONE instance I remember having great sex when I was on top, but I've never been able to replicate it. I'm TERRIFIED of it now. I feel super self conscious which probably doesn't help a lot. Also, ever since then it tends to slip out and that just kills the mood. So what the heck am I doing wrong? It's almost like I can't get in a good enough position to have the leverage to grind or anything.