can't delete the frames I want (the white dots)

Thank you for the Video.

I don't know how to get rid of the "white Dots"  in particular. I can remove them but not those I want. The frames (Illustrated as white dots) don't make sense to me. I can not figure out the behaviour with the shortcut "e". I can manipulate them but not the way I want them.

e.g there are two frames between Keyframe 4 and 5 I can't get rid of. Also on the top, there is one between 1 and 2... when you said, delete the frames on top, how do you do that exactly?

and why does it "skip" frames (white dots), when I move with the arrows to the left or right? In other words, why do I have semi frames? Are those semi frames?

Hopefully, you will find a way to explain this to me...

thank you

Martin