Sidebar
On the left side of the main window is the Sidebar with the two main sections.
Main Menu

On top is the main menu. The image above shows that the Trekking Panel is selected. Below that you can select the Calendar, and NPCs.

Above you have the sidebar disclosure button that lets to hide or show the sidebar. For a two-page character view it's often a good option to hide the sidebar (just be sure to select the character first!).
Characters & Groups
Below the main menu is the CHARACTERS section, which is the default group for all characters. If you defined groups these will be shown below that.

Version
At the bottom of the sidebar is the version and build number of the application that is currently running. The P stands for 'Public', as this is the public version of the app. This is followed by the version number (1.1.0), and in parenthesis, the build number (78).

