how to caput the id of a case in bonitsoft

Good morning the reason of my question is about how to capture the id of the case in pretty soft I am using a form 6.x when looking for information on how to perform the procedure I do not find information easy to understand I am new used the program if someone knows how you can perform the process or where you can find information about the topic so you can start programming because you do not know where to start. I am used groovy editor