Remarks are used to leave notes for others that may need to modify a file. An old programmer's trick is to remark out a line when editing a file so the editing can be undone easily if needed. They also put all options in the file and remark out the ones they don't need at the moment.
Nothing.
It does absolutely nothing.
rem is short for "remark", and anything that follows rem is ignored, because it is all just a long remark.
