Use the word "extreme" for a situation involving very strong qualities that are very intense and very different from what is normal or average.
Extreme weather comes in the form of tornadoes, hurricanes, and blizzards (heavy snow with wind).
Extreme heat can cause crops to fail.
Extreme behavior includes yelling, punching, kicking, or screaming at another person.
A person whose political beliefs are far outside the norm might be labeled as extreme, or that person might be called an extremist. (The word "extremist" is a noun.)
Mountain climbing, parachuting, and surfing are extreme sports. (They’re dangerous sports.)
Skydiving (parachuting) is an extreme sport.
The phrase "go to extremes" means that a person or an organization does something that is radical or very out of the ordinary. Here are some examples:
Joe goes to extremes to stay in shape. He works out at a gym three hours a day.
The company went to extremes to keep itself in business.
Maria goes to such extremes to keep from gaining weight, it’s a little unhealthy.
The government is going to extremes to prevent certain people from entering the United States.
The word "extremely" is an adverb. It’s similar to the word "very."
The Freedom Tower in New York City is extremely tall.
Skydiving (parachuting) is an extreme sport.