A commercial property policy pays to repair the building. Business interruption pays for the trading you could not do while it was being repaired, and on this coast that second figure is frequently the larger one.
What triggers it
Almost always, direct physical damage to your property from a covered peril. That is the sentence to hold on to, because it explains the answers that feel unfair afterwards. If your building is untouched and you closed because there was no power, or because nobody could reach you, the main trigger has not been met.
Two extensions deal with that. Civil authority cover responds when an order from a government body prevents access to your premises, usually for a limited number of days and often requiring damage somewhere nearby rather than to you. Utility services cover responds to an interruption in power, water or communications, and is frequently optional, frequently sub-limited, and frequently absent from the policy of the business that most needs it.
The waiting period, and the limit
Most policies carry a waiting period, commonly 48 or 72 hours, before the coverage begins to accrue. That is not a deductible in dollars; it is a deductible in time, and after a widespread event it removes the first days entirely.
The limit is the other half. Business interruption is generally written against a period of restoration and an income figure, and an income figure set from a quiet year does not rebuild a seasonal Naples business that makes most of its money between January and April. Bring us your actual seasonality and we will size it against that rather than against an annual average.