General Liability Insurance is something small businesses may need. Often it is requested by a customer (or the company hiring you as a contractor).
General liability insurance is designed to cover any loss (damage) that may result from an accident caused by you while you are working in someone else's place of business.
Proof of General Liability insurance is conveyed on an "Acord" form. This is a form that they insurance company will make. This is not a form that you get to fill-out.
Your customer will want to be listed as a "Certificate Holder". And, they might also ask to be an "Additional Insured". Each Acord form is made individually for each requesting customer (your customer).
The insurance premiums will vary widely depending on the type of business. The greater the risk, then the higher the premium.
Business General liability insurance is NOT the same as Errors and Omissions insurance. People sometimes get these confused but they are very different things.