Custom Drop-Down List is one of the form types defined in the system. It includes the following drop-down list.
In the design page, you need drag the "Custom dropdown list" item in the left panel and drop it into the center panel. It will allow you to create a custom drop down list.
Select one of the defined object in the page, this field will be linked to the selected object. For example, the manager field in above example will be linked to the specific organization users in the system.
A new form field can be linked with other form field. In this way, two forms can be linked together. See the following example for the form field linked dropdown list.