Is it possible to define a form on a start event?

Hello there,
is it possible to define a form on a start event?

In modeler on start event, form is available. My question is, for what it can be used if is possible to define it on start event?

Thank you.

Yes. If you define a form , on start of the process instance a form will be available where you can submit the data that will be available as process variables in your process instance.

Starting from Camunda Tasklist → Start Process?
What if I start process instance programatically using runtimeService?

Yes. Java API has the option to fill in the form

Like passing variables or in some other way?

@hedza06 to submit a form data through api, you can refer this page Submit Start Form.