What is the difference between an alert and a control?

An alert notifies you of transactions on your account. A control determines if the transaction will be denied or approved.
Alert Example: If you enable (turn on) an alert for Restaurant Merchant Types you will receive a text if your credit/debit card is used at a Restaurant.
Control Example: If you enable Merchant Controls and do not keep the Restaurant category turned on, your card will be denied at restaurants.