Learn French: En automne, il fait froid le soir. - In autumn, it is cold in the evening.

In French, we use the verb faire (to do/make) for weather conditions, not être (to be). So, il fait froid literally translates to "it makes cold," which is how French speakers say "it is cold."

Why do we say en automne for "in autumn"? Do all seasons use en?

We use en for seasons that start with a vowel or silent h: en automne, en été (in summer), and en hiver (in winter). However, the word for spring starts with a consonant, so we use au and say au printemps.

Why does le soir mean "in the evening"? Where is the word for "in"?

In French, placing the definite article le before a part of the day or a day of the week shows that an action is habitual. There is no direct translation for "in" here; le soir simply means "in the evening" or "evenings" in general.

How would I use the grammar from this lesson to say it is cold "every evening" instead?

You would replace le soir with tous les soirs. Because soir is a masculine noun, you use the masculine plural form tous, followed by the plural definite article les.