Arrange the palettes of the User Interface in a way that best fits your workflow.
This video demonstrates the following:
When you install Revit, the Project Browser and Properties palette windows display in a docked or locked position, one above the other. The MEP System Browser, and Reconcile Hosting windows are also dockable windows.
To undock a window and make it a floating palette, click in the title bar of the window and drag it into the drawing area. You can even move the window to a second monitor if you wish.
To display more of each window without taking up additional screen space, you can dock 2 or more windows as a tabbed set.
When moving dockable windows, it's important to pay attention to the cursor position and the visual cues. With the cursor in the title bar, drag the window until the cursor is touching the edge of the Revit interface where you wish to dock the window. The outline of the window gives you a preview.
Now, using the same method, drag the second window. Position the cursor on the lower edge of the title bar of the docked window, and notice in the preview of the window that the palettes will stack as they were originally. If you position the cursor within the title bar however, above the lower edge, the palettes will display as overlapping tabbed windows.
Click a tab to change focus to that palette. To separate tabbed windows, click the tab and drag the window to the drawing area. The other window remains docked.
You can also dock palettes one next to the other.
To dock 2 palettes in the same horizontal space, move the window, positioning the cursor to the inside edge of a docked palette. Adjust the widths of the palettes as you wish.
If you watch the cursor and the frame preview when moving dockable windows, you can position them to help you work most productively.