I have some questions.

What is the "display" variable in Quick Engine sprite objects?If 0,does it not display the object because when I tried its not working.

How do i use "atan"?Like this?

atan(math stuff)

Yes this was the intention, but the implementation was missing. I have fixed the lib, you have to remove quick engine from your project and then import it again and the display field will now work as expected! Thanks for reporting this.

atan is a function thus you can call it as any other math function, as in pi = atan(1)*4

And the "angle" variable from Quick Engine,what is it?

You mean line 201-203 in Quick Engine code? It is just for internal use, a random direction for the camera shake feature. Sprites have a rotation field if you want to rotate them.