Learn French: En avril, il fait chaud.

When talking about the weather, French uses the verb faire (to do / to make) rather than être (to be). So instead of saying "it is warm", you literally say "it makes warm" (il fait chaud).

Does chaud mean "warm" or "hot"?

It means both! French uses the same word, chaud, for both "warm" and "hot". You have to guess how hot it is based on the context or the season.

Why isn't the month avril capitalized?

In French, months of the year and days of the week are always written with lowercase letters. They are only capitalized if they happen to be the very first word of a sentence.

Why do we use en for "in"? Could I use dans instead?

When saying that something happens "in" a certain month, French always uses the preposition en. So you will say en avril (in April), en mai (in May), and so on. You wouldn't use dans for months.