When a window is first selected or created, that window moves to the top and is active while all other windows become inactive. You can only work in the active window. Four different methods allow you to move between the window classes:
1. Click on the appropriate window button on the Toolbar.
2. Press Ctrl + Shift + Tab to cycle among the window classes.
3. From the Windows menu, select Pop Build Forward, Pop Output Forward, Control Panel, or Subscript Control.
4. Use the mouse and click on the appropriate window (this only works if the window is visible).
The last method works particularly well for the Build Window, which is the largest and is not usually covered when other windows are active.