Some user interface elements (such as toolbars and some dialog boxes) can dock themselves into the Edit window or the toolbar area when you drag and drop the item on top of one of those areas. If you don't want this, hold down the Ctrl key while you release the mouse button. The toolbar or dialog box then hovers over the dockable background instead.
Some items, such as the Edit window, contain a right-click menu item (Docking View) that allows you to dock or undock that item. If the right-click menu item is not selectable, close any open dialog boxes and try again.
You may need to cascade (Window | Cascade) or tile (Window | Tile Horizontally or Window | Tile Vertically) your windows and then click and drag a window's title bar to float one over another.