Don’t go out tonight. It __________ outside.
The first sentence is an imperative sentence with the structure “Don’t + Infinitive” to advise, command or suggest someone to do something.
In the second sentence, the verb is conjugated in the present continuous with the structure “am/ is/ are + V-ing” to express an action that is happening at the time of speaking. The verb to-be in the third person plural “it” is “is”.
Translation: Don’t go out tonight. It’s snowing outside.