Custom fields allow you to create your own fields which you want registrants to be able to fill in. These fields can be filled out on registration or through the delegate profile in the back end or front end.
Head over to the 'delegate' section under your chosen conference. When you click it, a drop-down menu will appear. Find 'Custom Field' and click onto it.
You will then find yourself in this page
To create a custom field, click on one of the options. This will create that field in the box below, from where you can click the edit button in the right corner.
You will see this pop-up:
The function of each input field is outlined below it's title