Enter the name for the custom field field

Select the object where the field should live

Pro Tip!
Fields that live on the Customer object should be high level fields like website, address, etc. 
Fields that live on the Map object should be specific to the onboarding like products purchased, contract amount, etc. 

Select the type of field. If you choose "Select" or "Multi-select" you'll be able to add the option. 

To see the custom field on the Map level, navigate to the Map, then click "Map Overview"

On the customer side, select the customer and then select "Customer Overview"

Here is the Map custom field that we just created

You can always toggle fields on and off within the Custom Fields settings