Most commercial transactions are governed by a very detailed and well-established body of rules that have evolved over a very long period of time, it being the case that governing trade and commerce was a strong driving force in the creation of law and courts in Western civilization.
As for other laws that regulate or impact businesses, in many countries it is all but impossible to chronicle them all in a single reference source. There are laws governing treatment of labor and generally relations with employees, safety and protection issues (OSHA or Health and Safety), anti-discrimination laws (age, gender, disabilities, race, and in some jurisdictions, sexual orientation), minimum wage laws, union laws, workers compensation laws, and annual vacation or working hours time.
In some specialized businesses, there may also be licenses required, either due to special laws that govern entry into certain trades, occupations or professions, which may require special education, or by local governments. Professions that require special licenses range from law and medicine to flying airplanes to selling liquor to payday loans to selling investment securities to selling used cars to roofing. Local jurisdictions may also require special licenses and taxes just to operate a business without regard to the type of business involved.
Some businesses are subject to ongoing special regulation. These industries include, for example, public utilities, investment securities, banking, insurance, broadcasting, aviation, and health care providers. Environmental regulations are also very complex and can impact many kinds of businesses in unexpected ways.