can i use jotform with my backend?

I have a backend where i would like to make some calculations with the data on the forms i create with jotform, can jotform send the data the user inputs in the form to my backend to use that data for my calculations? Would it be like a normal get/post method?

Yes, you can use the GET POST method as explained here: https://www.jotform.com/help/213-send-submission-data-via-post-method-and-thank-you-settings

Or you can integrate the form with Webhooks: https://www.jotform.com/help/245-how-to-setup-a-webhook-with-jotform

I have moved your last query regarding creating a bill to a new ticket link: https://www.jotform.com/answers/2722833