Further to what MLeek said...
Business is about finding an (unfulfilled) need, convincing prospects that you are the one to fill that need, and to do it effectively/efficiently enough to make it worthwhile.
OR creating that need!!! You don't have to re-invent the wheel, you just have to create a need in your prospective customers for YOUR wheel and only your wheel.
Retail is servicing the public, which implies many small transactions. There is a wide range of possible price-points, ranging from boutiques (customized, relatively high margins) to commodity (standard product, very thin margins, reliance on high volume). At each price point, it is possible to make money, but the marketing, process of delivering the product, expected transaction volume, and investment in equipment/administrative systems/procedures/training is very different from level to level. Figuring out which segment you are best equiped to serve is not a trivial task. Learning about business gives a prospective business person some basic tools (and even an MBA gives only basic tools) to determine which components of the business model are relevant to their situation, and once the basic organization is done, to customize one's activities and processes to the specifics of the niche market they are trying to serve.
I run several businesses, and have, over the years worked in and with businesses ranging from multinationals, to one-person specialty shops. Probably the most frequent reason for going out of business is the lack of sufficient planning. The second most common reason is lack of sufficient financial resources. Third most common is not managing the cashflow. Over the longer term (10 years or more), businesses fail by not adapting to changing circumstances.
Keith (KmH) often refers to links discussing the business plan. MLeeks has referenced several links with very good business advice. The foundation of any business has to be a well-thought out business plan, which starts with a deep and detailed look at the prospective market one wants to exploit. What are the existing characteristics, buying patterns? Who are the preferred suppliers to that market? Is there an untapped potential in that market? Who are the "heavyweights" in that market, and why are they successful? Are there any societal/environmental trends that may change the dynamics of that market?
Once the market is researched and understood, the next challenge is to determine how to generate prospects in that market. What are the characteristics that define the most valuable prospects within that market? What/who are the authority figures that these ? the influencers? Which media do the prospects use to find the services they want? Where they shop/eat/entertain themselves? What are their "hot buttons"? Assuming that you reach them, how do they contact you? What is the process you use to log and follow up your prospects? How many steps are there before a signed contract is obtained? How do you follow up with the prospects that did NOT go with you, and what can you learn about why you did NOT get their business? Are there direct competitors who are winning away your most valuable prospects? If so, what are they doing right that you are not?
Once you have a contract, what is the process for ensuring a smooth production? How do you identify, quantify and minimize risk? Tim Campbell did a very good writeup in another thread (on weddings) where he described some of the prep work needed for a wedding. Each production project needs to have a similar level of thinking and planning. How do you cover equipment failure? How do you minimize communication failure? Do you have a plan and schedule for the event(s), the post-production, and the final delivery? What measures are you taking to ensure that you get paid?
Once the contract is complete, do you have a plan for the post-mortem? What went wrong, and what could have been done to prevent it in the first place? What opportunities presented themselves for new business? Are you dealing with the most valuable prospects, or do you have to re-evaluate that? What about your production efficiency - which activities took more time investment than you planned? Why? What could be done to improve the effectiveness? What changes to the process can you see to improve the client experience? to improve the marketing prospects? to reduce risk?
What administrative processes are you planning/using to stay on top of commitments? what followup are you planning/doing to ensure your investment in marketing is not wasted? What is your cashflow projection and how does your actual cashflow compare to your projections? What has to change to improve the cashflow?
and so on.
On the financial side, there has to be enough financial reserves available to buy/rent the production equipment needed, pay for operating and living expenses for about 6 months, and to remit to the various levels of government the appropriate permits, taxes, fees that need to be paid by a operating business, to pay for (some) legal advice and paperwork, and to cover (some) accounting services. If you've borrowed money to start the business, then the financial costs and available credit must be carefully tracked and managed.
And then there's the daily monitoring of the cashflow. You had a plan, how's it actually working out? Are you getting enough revenue in your bank account to match your cashflow projections? Are your collection timelines reasonable? Are your outflows all budgetted or are there many unexpected drains?
Business can be both fun... and when things go wrong, they usually go really, really wrong in a hurry. Business is not for amateurs.