NOTE: Changing system function key preferences affects how the function keys work for your Mac, not just Excel. After changing this setting, you can still perform the special features printed on a function key. Just press the FN key. For example, to use the F12 key to change your volume, you would press FN+F12. If a function key doesn't work as you expect it to, press the FN key in addition to the function key.
If you don't want to press the FN key each time, you can change your Apple system preferences: Change function key preferences with the mouse. On the Apple menu, press System Preferences. Select Keyboard. On the Keyboard tab, select the check box for Use all F1, F2, etc. Keys as standard function keys.
Although Microsoft did not include many keyboard shortcuts in their Office Suite for Mac, you can make your own for any app including Office apps. To do so: Go to System Preferences and then Keyboard. Select the shortcuts tab.