The top half of the screen is where you enter the Input Specifications that are used to tell Disk Triage what to include in the Sizing and Analysis. You click on the Input tree to the left - to change the Input forms in the Input Docking area to the right. Once you have entered the information you want - simply hit the 'F2' key - or - click on the icon in the upper left of the tool bar to start the sizing.
The bottom half of the screen is used to display the Sizing and Analysis Results. Here you can view the Tree, Graph, Drive Info, Analysis views, etc. In the above screen shot the bottom Docking Area is configured to allow two windows - however, by default, when installed it only allows one window to be docked there. Each Windows in the docking areas can be undocked, allowing the user to use multiple views at once.