Dropdown lists are used when you want users to pick from a list of options.
Create your form using the Forms for Confluence macro.
Add the Forms - Dropdown List macro in the body of the Forms for Confluence macro.

Set a Label for the list, this will appear next to the checkbox options.
Set a Name for the list.
Optional: Set a Description for the list.
Optional: Select the Required checkbox, if you want this as a mandatory field in the form.
Define list options, by giving a Label and Value.
To add more options, click the "+" sign and fill in the fields.

Save the macro to see a placeholder box in the order fields will appear on the saved page.

Save the page to see the final field on your form.
