Learn German: Draußen ist es kühl und windig. - Outside it is cool and windy.

In German, the conjugated verb must be the second idea in a standard sentence. Because this sentence starts with the location word draußen (outside), the verb ist (is) must take the second spot. This pushes the subject es (it) into the third spot. If you started the sentence with es, it would be: Es ist draußen kühl und windig.

Why does the sentence use es (it) here?

Just like in English, German uses an impersonal es (it) to talk about the weather or general conditions. Instead of naming a specific thing like "the weather" or "the air", you simply use es as a placeholder subject.

Is there a difference between kühl and kalt?

Yes! Kühl means "cool" (a bit chilly, sometimes pleasantly so), while kalt means "cold". So this sentence describes a chilly, breezy day, but not a freezing cold one.

Why don't kühl and windig have any extra letters added to the end of them?

In German, adjectives only get special grammatical endings (like -e, -er, or -en) when they come directly in front of a noun, like in the phrase "a cool wind". Because kühl and windig come after the verb ist and just describe the general condition, they stay in their basic, unchanged dictionary form.