' literal denotes a comment in Visual Basic. When the Visual Basic compiler encounters a comment, it ignores everything it.
E.g:
'The following line displays the obligatory "Hello, World!" message to the user !
MsgBox ("Hello, World!")
The first line is completely ignored by the compiler as it is meaning-less to it. Visual Basic, unlike a few other languages doesn't supports multi-line comments, so you have to comment out every-line by hand (which is annoying obviously). Visual studio provides support for commenting out multiple lines at once. You can do this by selecting the lines you want to comment out, and then pressing CTRL+K and then CTRL + C.