Can someone actually explain?

Hit the power button to hang up.

Can someone explain?

I believe accept/decline is when your phone is inactive, slide to answer is when you're using your phone already

depends if your phone is unlocked or not

When dad calls vs when mom calls

When you phone is locked you get the slide to answer option, and if it's not you can accept or decline the call.

Is it a apple?

Then your phone is locked is has the slide to answer but when your option is unlocked or if you are on it it gives you the choice :)

It's whether your phone is locked or unlocked.... I have an android and even I knew that