The User Guide is a tool that allows you to browse the inline user guide and other help related to the simulation. It explains the interface and some of the concepts of the Mars Simulation Project.
The window keeps track of your path through the guide. The 'Home' button returns you to the starting user guide page. The 'Back' button returns you to the page you previously visited. The 'Forward' button sends you back to the next page, if you have gone back.