Sadly, Windows Phone is pretty much dead, so I'm no longer maintaining this project. If Windows Phones ever makes a comeback, maybe this will, too.
First off, you're going to need to have the Windows Phone SDK.
To test out the Dropbox sync functionality, you'll need a developer API key from Dropbox. Put this key in the file called 'apikeys.txt' in the main folder of the application and set its build action to 'Resource'. The file is in JSON format, like this:
{"dropboxkey":"..."}