Social media marketing is the act of informing people about what your business is all about; it's that simple. I know it doesn't SEEM simple, but think of it like this:
Driving a car is the act of getting from one place to another. Is it that simple though? If you've never driven a car, it's not simple at all.
There is a lot to learn before taking on either endeavor.
Do you remember driver's ed? They didn't just put you behind the wheel and say "Go!" It consisted of many components that needed to be understood before getting into a vehicle.
The same approach applies to learning effective social media marketing. You can't learn how to effectively market online without first learning many components including "why?"
Not just any "why" - your "why."
When you are crystal clear on your message, you will be able to convey it to your followers. Social media marketing is, after all, just a form of communication. Social platforms like Facebook and Instagram are simply communication channels.
The rest of what goes into it is marketing, and the best practices that you already use for your marketing efforts apply. Sure, marketing online requires a bit of technical savvy, but I maintain that if you can work a smart phone, you can perform social media marketing for your business.