California residents may choose to start their own business either as a main source of income or as what some people refer to as a "side hustle". However, it is important to understand that even small businesses run from a home are not necessarily exempt from following the law. Depending on what type of business a person chooses to run, he or she may be in violation of zoning or other laws that forbid it.
Local libraries or government websites may describe in detail what types of companies are allowed and which ones are not permitted. Those who run their business from their condo or home within an HOA may want to study association rules carefully before they begin operations. Members of the HOA board itself may be able to tell a person more about any applicable restrictions.