Betty,
In addition to Norman's comments, you can switch between the two (or more)
open workbooks with Window (Menu bar). Or use Ctrl-Tab for a keyboard
shortcut. Or if you've used the Windows in Taskbar option Norman mentioned,
you can click on the workbook you want in the taskbar.
The bottom line is that when you open a workbook (or start a new one), it
adds another open workbook. They remain open until you close them.