Following along in MyCase is recommended as you read the steps:
The Single Select Custom Field lets you create a list of pre-defined items. When creating or editing a case, contact, or company record in MyCase, you can choose an item.
How to Create Single Select Fields
When adding a Custom Field into MyCase (learn more)
Name the Custom Field
Choose Single Select as the field type
Click Add list option.
Type a List Option into the box
Press the check mark
Repeat until you've added all the options you'd like
You can re-order the list options by clicking and dragging them up and down
Once everything is added and ordered correctly, click Add Custom Field.