Help I'm new

Hello, as stated above. I'm new to this and have no idea what I'm doing. This probably would have been easier if I'd learned to drive a stick. But I don't even have that base knowledge. I've tried watching a ton of videos, but none of them are really answering my question.

So here's my question. Can someone explain rpms and how it relates to shifting and the speed of the bike. I'm comfortable enough to ride in second here but going any higher than that I'm scared of going too fast. (This is my first bike and I'm the only one in my family to ever have one so please don't think I'm stupid. I'm just new)

I'm not really sure what rpms are or how it relates. I just keep hearing rpm this and rpm that. I don't want to burn up my clutch which I think I have been in an attempt to ride safe. But when I shift from first to second getting the throttle to the right speed feels weird and there's like this bump / big feeling. Same thing when down shifting. Idk. I'm just trying to understand better.

Thx for help in advance

Oh, and I'm riding a Kawasaki ninja 400 if that gives you any important info 👍