CodeSnipppets allows you to create a 'library' of snippets of code that you want to resuse.
For example, lets say that you start each program with an elaborate comment. Rather than have to type it over and over, you simply highlight the comment (or any number of lines) and drag it into the codesnippets window. It will then allow you to give it a name.
Open a new file and double click on the name you chose for the snippet, and it will place that code at the cursor.
Its like a clipboard that can hold any number of 'snippets' of code that you can reuse at anytime.
Very useful!