Does anyone know how to conduct market research properly?

I want to build a social media network for affiliate marketing but I have absolutely no idea how to do it. What do people need? What products are trending? Which products are hard to sell and have become saturated? What are the popular sales channels? Who is my target customer? There are so many questions, and I can't find any reliable source of information other than paid tools like the ones I used to use at my company. Does anyone know of a reputable source for this information? Or do you have experience researching and finding this information?

If you don't have answers for any of those questions you're poised to fail..... don't start business concerning stuff you have no idea about, do research, and know everyting about a thing before starting to turn that thing into a business