Used lines will be marked with green, unused ones with red.
You can get the same coverage data from Chrome Developer Tools too,
Just because a line is marked as unused, it doesn't mean that you can remove it completely.
Some parts of your code might be accessed after a user interaction like clicking on a button, submitting a form, scrolling, resizing the window etc.
Code parts that are needed in other browsers than Chrome will be marked as unused as well.
Test your changes thoroughly in different browsers and on multiple devices before applying them to a live site.