Click on the cell you'd like to add a dropdown list to.
Click on the "Data" tab.
in the "Data Tools" section of the ribbon, click the arrow next to the data validation icon.
Click "Data Validation..." in the dropdown.
Click on the dropdown for "Allow."
Click on "List."
Click on the "Source" dropdown.
Type the text you'd like in your dropdown list.
Click "OK."
To view your new dropdown, click on the arrow in the cell you've added the dropdown to.