Potty Training

I have a 22 month old boy. We’re trying to potty train but he hasn’t seemed to grasp that he has to go potty in the big boy potty instead of his underwear. He says a few things & I explain to him that he needs to use the potty and not go in his big boy underwear. Not sure if he understands but he understands most things so I explain to him every time that he’s suppose to use the big boy potty & not his underwear. He loves going to the bathroom with his daddy, me or his grandma. He knows what to do. He knows he sits on the potty, wipes, flushes & washes his hands when done. I just don’t know why he doesn’t use the potty. I know it takes time. Guess I’m just looking for opinions on what to do or even stories on how you’ve potty trained a boy. We’re not potty training standing up until he knows how to go sitting down. Also, how did you go about potty training & nap time && bedtime??