I suggest you use a template like the Lean Canvas to help you get started and validate any assumptions you may have.
I’m linking to a website that has information on this below, from which you can download the lean canvas template.
There is also a great book called The Lean Startup by Eric Reis, which gives a good overview on starting a company in an efficient and effective way. https://www.amazon.com/dp/B004J4XGN6/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1
I hope that helps, good luck!