This is how to add a custom field:
1. Menu (left)
2. Setup
3. Custom Fields
4. You will see a list of all your current custom fields
5. Create new [+ New Custom Field] (or edit a current one by clicking on it)
6. Select the area where you want the custom field to appear (*Field Belongs to)
7. Add or edit the *Field Name
8. Add a "Type" i.e. Text Box (big box), Input Area (small box), Multi Select e.g.
9. If you see an "Options" box, you will have selected a "Selector" field type or "Multi Select". The options you wish to see in the box of the custom field, you will need to seperate each option by a comma.
10. You can leave all the tick options.
11. Save