When you remove your dog's leash so she can run wildly across the beach, you unleash her — you set her loose. And when you unleash a storm of insults against your brother, you allow them to flow freely from your lips.
There are two ways to use the verb unleash. Literally, it means "set loose," like when a police officer unleashes her trained dog to sniff luggage for illegal drugs, or a farmer unleashes her llama after moving it into a pen. Figuratively, you can unleash all kinds of emotions, forces, opinions, and actions. Unhappy citizens might unleash a series of high-profile protests, or a barrage of shouted demands, for example.