An HO-3 policy is the most common form of homeowners insurance. It covers your home and other structures on an open perils basis, meaning you're protected from any cause of damage unless it's specifically excluded.
Your belongings are insured on a named perils basis, so they're only covered if the damage is caused by events listed in the policy. For example, if a car crashes into your fence, the policy would cover the damage. But if your home is damaged by a sinkhole and sinkholes are excluded, the loss wouldn't be covered.