A drop down field will display a list of values in a drop down list to users. Users can select one of the values.  To specify the values that appear in your drop down list....

Click the Data Tab

In the section "Data Source Values" enter your choices in the Label Field.  The "Value" field will autokmatically be filled in for you.  Both Label and Value are both required for each option.  If you want to change the value to your own custom choices, that is perfectly fine.