Learn French: Il fait chaud à l'intérieur.

When talking about the weather or the temperature of a room, French uses the verb faire (to do/make) instead of être (to be). So, il fait chaud literally translates to "it makes hot", which is how French speakers say "it is hot" or "it is warm".

Since this lesson is about prepositions with de, why isn't there a de after à l'intérieur?

If you want to say "inside of" a specific place, you do use de: à l'intérieur de la maison (inside the house). But in this sentence, we just say "inside" without naming the place, so the de is dropped. The same rule applies to phrases like à côté (nearby/next door) vs. à côté de (next to).

Does chaud mean "warm" or "hot"?

It can mean both! French uses chaud to cover both "warm" and "hot" temperatures. You can usually tell how intense the heat is from the context, or by adding words like très (very) or un peu (a little).

What is the literal meaning of à l'intérieur?

It literally translates to "at the interior". It is the most common way to say "inside" or "indoors". If you wanted to say "it is warm outside", you would use its exact opposite: à l'extérieur.