Once installed, a new item called Authors is added to your Admin Menu. Below that item you will see the Settings option. Click on it to open the plugin settings page. There you have all the options you need to configure how you want the plugin to work. Keep in mind that some of those settings can be overridden by more specific post and user settings —available on their edit screens.
For you convenience, plugin settings are grouped into tabs: Author Box, Guest Authors, Co-authors, Users, More, Advanced and Shortcodes.
This tab holds all the settings related to the premium license. This is where you have to come to set your license key in order to activate your key.