Using a workspace file
If you usually work with a number of workbooks simultaneously, you might like the idea of opening all of your workbooks exactly where you left off the last time you closed Excel.
If so, you need to create a workspace file. Before you quit for the day, select Files, Save Workspace and specify a file name. To pick up where you left off in the last session, reopen the workspace file: Use File, Open and choose the workspace file (it'll have an .xlw extension).
Note: A workspace file contains only configuration information, not the actual workbooks and worksheets. Therefore, you can't simply copy the workspace file -- you'll need the workbook files, too.