Learn Spanish (Latin America): Cuando hacía frío, preparábamos suficiente leña para el fuego. - When it was cold, we prepared enough firewood for the fire.

Because this sentence describes a repeated past habit, which is exactly what the imperfect tense is used for. The word cuando (when) sets up the recurring condition (whenever it was cold), and preparábamos tells us what we repeatedly did in response (we used to prepare).

Why is it hacía frío instead of estaba frío?

In Spanish, you use the verb hacer (to do/make) for most weather expressions. To say 'it is cold,' you say hace frío (literally 'it makes cold'). To say 'it was cold' as an ongoing or repeated condition in the past, you use the imperfect tense form: hacía frío.

Why does suficiente come before leña instead of after it?

Most adjectives in Spanish go after the noun, but adjectives that express quantity or amount (like enough, much, little, some) almost always go before the noun they describe. Since suficiente means 'enough,' it goes right before leña (firewood).

Why do we use para instead of por in para el fuego?