I just watched the evernote video and am very impressed with what it can do. However, I would be surprised if you could write this in "a function". This product runs as a browser extension and supports all browsers, so the first thing you need to do is study how to create a BE. Once you have a simple BE running you can start thinking about the ways you would capture the data from the web pages that the user clicks on. Then you need to figure out how and where you are going to store this information, etc.
One of these days I'm going to think of a really clever signature.