Shell shift procedure - What is this?

Question

In shell we have the command shift, but i saw on some example its giving shift 3

Why there is a number after shift ? and what its about ? what it does ?

Example:

Answer 1

shift treat command line arguments as a FIFO queue, it popleft element every time it's invoked.

array = [a, b, c]
shift equivalent to
array.popleft
[b, c]
$1, $2,$3 can be interpreted as index of the array.

bash - The advantage of shift over reassign value straightforward - Stack Overflow