This is quote. There is no computing. Just return itself.

'(list a b)
=>(list a b)

Backquote + Comma

This is a backquote to return itself, but you can use , to computing inside.

`(list ,(car (list 'a 'b)) b)
=>(list a b)

Comma + At

The expression will be expanded in place. Useful for dynamic arguments.

(setq a (list a b))
`(list ,@a)
=>(list a b)