How do I create a Custom Field from the the Flow Tool?
Click the Process(es) Tab (in the Flow Configuration Tool).

Click the (+) Add button, beside the Field Type(s).

Complete the Info section. Items with an asterisk are required, everything else is optional.

Click the Add Trigger button.

Complete the Trigger entries and selections, then click the Save button.
Click Save.

Congratulations, you created a Custom Field!