Billing is more focused on issuing invoices and tracking payments, while payment processing is mainly about taking payments and transferring them into your have account. Make sure you understand this distinction when a running your business so that you will know what you need and use the right software for the job.
A function is a goal that can be accomplished with a product, service, process, practice, system, application, document, component, machine or environment. For example, an aircraft that can land. A feature is a tool that helps to functions.
Tutorial videos can show how to use software, perform a dance move, play an instrument, apply makeup, or anything else your audience wants to learn. The primary goal of a tutorial video is help to guide the viewer through a particular activity so that they can complete it themselves.