You can close interventions by clicking on "Close sheet". Afterwards you can do two things:
Create a new intervention: if not all tasks are done or not all products are delivered, you can create and plan a follow-up intervention.
Create an invoice by clicking on the Actions button "Invoice".
You will be redirected to the Invoicing module. Depending on the type of invoicing you have chosen and the delivered hours, products and services, you will receive an invoice proposal that you can validate and send to the customer.