When you go to your insurance agent to purchase comprehensive liability insurance, your agent will give you a binder. This is a document created by the agent. Generally, within 30 days or so, the actual insurance company will send you the insurance documents. Some insurance companies take longer.
The binder is not acceptable as proof of insurance. The Certificate of Insurance is acceptable showing information regarding the effective dates, amount of coverage, the location(s) covered and list the NSC as the certificate holder.