Questions about being a marketer.

I'm a teenager from Canada looking to start helping local businesses with marketing on Instagram. What I'm confused about is exactly what I would do and how I would do it. Here are my biggest questions:

How can I show that I'm worth it and that Instagram can bring in sales?

How much time do I need to work each week?

Usually, once you establish a business' Instagram do they let you go or do you keep working?

How do I communicate what I am doing on their Instagram to the businesses? Do I go to them in person or is an email enough?

How do I get the pictures? If I take them then do I take a lot in one day or go to the business regularly to take pictures?

Sorry for so many questions, I hope I can figure these things out!