Try right-clicking on one of the tabs and selecting "Insert." This will open
a dialog box. Select "Worksheet" and then you can name it what you want. The
right-click menus give you a lot of different options, like rename, move,
etc.
My input is based on Office 2003 so if you have a newer version you may not
follow exactly the same process.
I don't understand what you mean by a worksheet with many tabs? Do you mean
a workbook with many worksheets? If you want to insert an additional
worksheet, the command sequence is:
Insert/ Worksheet.