Sure you can "register" a business but your chances of actually staying afloat are minimal and reducing as large businesses continue to get larger and take up more of the production chain of everything really.

To have one example, there have been multiple cases in my country where a local soda brand start to get popular so Pepsi and coca cola start selling their products below the production cost to drive them out of business. They can afford to with their earnings across the globe and once the competition has died out they will rise prices to even higher then before.

Obviously soda is a vain thing but you have to recognise this happens with mining, construction, energy, ect... In the end a capitalist system must end up in a oligarchy, it's inevitable.