The username and password the plug in is asking for when you activate is a Wordpress.com account you'll need to create, so the stats have something to tie back to and track the stats to.

You will need to create an account if you don't already have one. We suggest creating a generic user account tied back to a generic school email, so that this can be accessed by any user at a later date.  Then, enter the username and password in when you enable the plug in to complete activation of the plugin.