Alerts are a great way to offer the user the ability to choose a specific action or list of actions. They also can provide the user with important information, or require them to make a decision (or multiple decisions).
From a UI perspective, Alerts can be thought of as a type of “floating” modal that covers only a portion of the screen. This means Alerts should only be used for quick actions like password verification, small app notifications, or quick options. More in depth user flows should be reserved for full-screen Modals.
Alerts are quite flexible, and can easily be customized.