In order to add a Field to your Cards, you'll have to add it to the Card Categories you want it to appear on.
eg, if you've created a DOB field, you may want to add that to the Crew Card Category, or the Talent Card Category, so it appears on every Crew or Talent card, but not the Location Card Category as you don't need to know a Locations date of birth.
To add your Field to a Card Category, go to settingsand then Card Categories
Select the Category from the dropdown menu or press + to Create a new one.
When you have selected your Category e.g. Talent, scroll down to "Linked Fields" and select the Fields you want to add from the dropdown menu at the bottom labelled "Choose a field to add".
Hit "Save" in the bottom right corner when you are finished to save the changes you have made to your category.