Using rules you configure Formulayt forms to react dynamically to user actions.
For example, let's say you are setting up a gate to collect registrations for an event. If a user indicates they have dietary requirements, we want the comments field to change its label to "My Dietary Requirements".
To do this, first, navigate to the comments field in the manage fields area. Then add a rule that states:
IF the field value for dietary requirements is yes AND the Form Type is Event Registration THEN change the label of this field to My Dietary Requirements. In Otherwise, perform these actions set it to Reset the label of this field back to its original value. Hit save and push the changes live or preview them to test.
It is important that this rule runs continuously so that it reacts in real-time to the user interacting with the form. 
By locating the relevant gate and previewing it I can see that my rule is working.
Got a specific requirement for field rules or having issues? You can get in touch by clicking New Support Ticket at the top of this page.