You can dock a floating window to the main window.
Click and drag the title bar of the window you wish to dock. Docking indicators appears automatically in the center, top, bottom, left, and right of the main window.
When the mouse pointer moves over one of the docking indicators, part of the window background becomes blue. If you release the mouse pointer at this point, the window will be docked in the blue area.
Selecting the indicators allows the window to be placed freely, as shown below.
You can also double click the title bar of the window or right click and select [Floating]. This docks the window at its former docking position.
You can adjust the size of windows docked to the main window by clicking and dragging the splitters.