ENGAGEMENT RING SHOPPING💍

So... My boyfriend and I have talked about getting married as soon as possible.. And we're looking forward to going ring shopping soon but how does that work exactly? Like do I buy his wedding ring when we go? Or later on closer to the wedding..? And when we go don't we just look at rings and get sized and all.. And then he'll have an idea of what I like etc.... And when he's ready to propose he'll choose the ring and he proposes with the diamond only and I wear that our whole engagement but he keeps the band... Right? Doesn't he keep the band and give it to me the day we have our wedding? And as far as his ring I don't even know how that works honestly. My mom's husband bought his wedding band but my boyfriend says that I buy it? Which I don't have a problem with ! I mean he's buying my rings ! So I'm okay with that I guess I'm just curious to know exactly how this all works and I wanna know how the ring shopping is and all!!!!! Help needed !!! Thanks in advance !!😊😊