Call to action

How to Add Action on button

i create on form and on text field 'cmnt'

I want to add a comment with a data from a form field 'cmnt' , I can add an action to the form and write the next groovy code:

apiAccessor.getProcessAPI().addComment(rootProcessInstanceId, field_TextField1);

for that i done following . now in submit's button's > general tab > action > add action now there is two field

---- takes value of ----- now exactly where i have to write code ?

i tried by ---- takes value of -Code = give error Variable -- takes value of -- Code = give error

How to use Call to Action / Sub processes ?

I need to call other process(es) from my main process.

How do I do that in Bonita BPM ?