Liability insurance is your overall protection policy for the business.
It covers if someone is hurt on your property or on a property where you are performing a service.
It will also provide you legal representation in the case of a lawsuit, and pay damages if you are found negligent.
Most property managers, marinas, parking garages, etc. require that you carry at least a million dollars in liability insurance to be able to work on their property. They will also ask you to provide proof of the coverage before you are given permission to begin.