Having a hard time using multiple fingers

So when I started playing I used a mouse, which obviously put a cap on how good I could get. So I started using keys, but started with one finger on each hand. Now a little bit ago I moved up to two fingers per hand, but I’m doing significantly worse. I don’t know if it’s me having bad fine motor skills, or what but I literally don’t know how to use multiple fingers for just the top/bottom. Does anyone know why or how I can improve/fix this?