Creating Custom Fields
Let's say we want to store the T-shirt size for our Contacts in Fleetio so we can send them a swaggy company shirt every now and then. Since there isn't a default Contacts field called Shirt Size, we would create a drop-down Custom Field with a label of Shirt Size.
In this case, we want to define the possible values it can have - (Small, Medium, Large, Extra Large, etc.). We wouldn't want anyone saying their T-shirt size was "Eleventeen", now would we? So we will choose the Drop-down data type to constrain the possible answers to our list of values.