To create a Field, go to Settingsand then select the Field icon

Press the plus sign next to the dropdown box to create a new Field.

Select the Field type you want from the "Field Type" dropdown box. This could be Choice, Multiple Choice, Date, Date of Birth or Text. Create a title for your Field, and then if you choose Choice or Multiple Choice Field, add values for your field. 

You can press the plus next to the last value to create another, and edit the colours of the values by clicking the coloured dot and choosing from a palette. Hit "Save" when you're done.

Add your new field to a card category so that you can attach these values to your cards.

To see how to add a field to a card category click here.

To see how to edit a field, click here.