I imagine that most people that have started businesses in the past did so without concerning themselves about theories. They just 'knew what to do' in general terms and then worked out the remaining details. Of course some of these businesses floundered or failed but some succeeded and some flourished.
We have now entered an age when more of us seem to have to think of ourselves as small businesses. Whether or not we welcome this is not really important. For a great many of us who are not 'natural' business owners the bigger issue is how we can structure the problem of describing a business that might provide income.
Someone on LinkedIn just asked for a definition of the term business model. I responded with a link to the corresponding wikipedia article from which I have drawn the following paragraph.
Whenever a business is established, it either explicitly or implicitly employs a particular business model that describes the design or architecture of the value creation, delivery, and capture mechanisms employed by the business enterprise. The essence of a business model is that it defines the manner by which the business enterprise delivers value to customers, entices customers to pay for value, and converts those payments to profit: it thus reflects management’s hypothesis about what customers want, how they want it, and how an enterprise can organize to best meet those needs, get paid for doing so, and make a profit.
I am not by any stretch a business person. Perhaps that's why I find this paragraph so useful. For instance, not every new service or gadget that you might invent will lead to a business; it has to match some perceived need for a customer. Or, you may provide great services but if you can't find an effective way of capturing customers for them you will never be paid for them. Or, is there an effective way of making customers pay for what you have done? By using this single paragraph you can verify the principal characteristics of a viable business.
That business might often be just alone you in an economy where permanent jobs are fewer.