Learn Spanish (Spain): Hace frío en la montaña.

In Spanish, weather expressions often use the verb hacer (to make or do) instead of the verb "to be". So, hace frío literally translates to "it makes cold". You will also see this in other common weather phrases like hace calor (it is hot) and hace viento (it is windy).

Where is the word for "it" in hace frío?

You don't need one! Spanish verbs change their endings to show who or what is doing the action. For weather phrases, the "it" is automatically built right into the verb hace, so you never need to add a separate pronoun.

Why does it say la montaña (singular) when the English translation says "the mountains" (plural)?

In Spanish, it is very common to use the singular la montaña to refer to a mountainous landscape or nature in general, much like we say "the countryside" or "the beach" in English. You can say las montañas, but la montaña sounds perfectly natural when talking about the environment.

If I want to say it is very cold, can I say hace muy frío?

No, you would actually say hace mucho frío. In this expression, frío is acting as a noun meaning "coldness". Because you are literally saying "it makes a lot of coldness", you must use mucho (much / a lot of) instead of muy (very).