Highlight the cell you want to format. Go up to the toolbar and click on
Format then cells.
Click on the number tab, then under category box go to custom.
Then in the box under the word Type, type in:

hh:mm AM/PM

Then click OK.

This will format the cell you chose to this. So when you type in 9:00 it
will come up as 9:00 AM etc.

Hope this helps.