Learn Swedish: På våren brukar vi städa huset. - In the spring we usually clean the house.

For habits or things that happen regularly during a season, Swedish uses på followed by the definite form of the season (våren, which means 'the spring'). So på våren means 'in the spring' or 'during springtime' as a general, recurring habit.

Why is the word order brukar vi instead of vi brukar?

This is the Swedish V2 (verb-second) rule in action! Because you started the sentence with the time phrase På våren, the verb (brukar) must take the second slot. The subject (vi) then has to wait until after the verb.

How does the verb brukar work in this sentence?

brukar is a very common Swedish verb that means 'to usually do something.' It works as a helper verb, which means the main action verb that follows it must be in its infinitive (dictionary) form without 'att' (to). That is why it is followed directly by städa, making brukar städa mean 'usually clean.'

Could we say på vårarna (in the springs) to show this happens every year?

You could, and it is grammatically correct, but på våren is the much more common and natural way to express 'every spring' in Swedish. For habitual seasons, Swedish strongly prefers using the singular definite form.