First of all since this is a beta, you'll need to join the Polarbearapp main community on Google+. Then you'll need to join the beta program. Which will allow you to have access to the application.
There's really nothing more to say. You know the purpose of the app and it's to allow you to post to whatever service that's available within one application.
The difference with version 2.05 from October 2013 is that the interface has been updated and has been improved over the previous. A more crisp and clean design which is more in line with halo.
Take note that this application doesn't pack features like crazy, at this stage it's made simple and clear.