With a sole proprietorship, you are the business. This is fairly simple. You won't risk large penalties by not filing such a certificate, but most banks insist you show the certificate if you want to start a bank account in the business name. You will be required to withhold tax, unemployment insurance and social security payments from your employees' paychecks, file tax returns and pay that money over to the tax authorities. Many other laws and regulations will potentially apply to you, depending on what business you are in.
Most states have sales taxes.
If you have a retail business, you will be required to apply for a special sales tax number from the state, collect sales taxes from your customers then pay the money to the state. Health and safety regulations may also affect you. Restaurants and food stores in particular are highly regulated. There is Always Opportunity. Chapter Home Life in the USA Home Page .