tabs

on a tab when u see --(13)---
....................-------- what do the parenthesis stand for???

When you see a note written like that, it's called a ghost note. Basically, it can mean one of two things - either the person who wrote the tab isn't quite sure whether or not that note is played in the song recording, or simply that it's an 'optional' note that they have added to make it sound a bit better. No big deal really. Hope this helps!