I did not realise you were on a Mac. There are differences from
Windows and I do not know what they are. Have never used one.

In Windows versions the Personal.xls is used in a similar way to normal.doc in
word. It contains macros  and other customisations which are available each
time you use Excel. It is opened as a hidden worksheet  each time  you open
Excel. If you want to change it you may need to unhide it. In Windows it
lives in C:\Documents and Settings\<username>\Application
Data\Microsoft\Excel\XLSTART\ I don't know where it is on the Mac.