Learn Italian: Oggi fa molto freddo, non esco. - Today it is very cold, I am not going out.

uscire (to go out) is a very common irregular verb. For the io (I) form, the first vowel changes from 'u' to 'e', making it esco rather than following the normal verb rules.

Why does the sentence use fa (it makes) instead of a word for 'it is'?

In Italian, weather is usually described using the verb fare (to do / to make). Instead of saying 'it is cold,' you literally say 'it makes cold' (fa freddo).

Where does the word for 'I' go in non esco?

You do not need to say io (I) because the -o ending on esco already tells us who is doing the action. Also, the negative word non must go directly in front of the verb. If you wanted to include the pronoun for emphasis, it would go before the negative word: io non esco.

Is freddo an adjective or a noun in this sentence?

In the weather expression fa freddo, the word freddo is actually a noun meaning 'the cold'. So, fa molto freddo translates literally as 'it makes a lot of cold'.