Learn French: Au karaté, on s'habitue à esquiver vite. - In karate, we get used to dodging fast.

The verb s'habituer (to get used to) requires the preposition à when it is followed by an infinitive verb. When learning new verbs like this, it is best to memorize the whole chunk: s'habituer à (to get used to doing).

Why is the verb s'habituer reflexive here (s'habitue)?

In French, the non-reflexive habituer means to accustom someone else to something. When you are getting yourself used to something, the verb becomes reflexive: s'habituer. Because the subject is on, the matching reflexive pronoun is se, which contracts to s' before the vowel.

Why does the translation say 'we' when the French uses on?

While on literally translates to the impersonal 'one', in everyday spoken French it is the standard, informal way to say 'we'. It always takes the same singular verb conjugation as il or elle.

Could I say Dans le karaté instead of Au karaté?

Au karaté (a contraction of à + le) is much more natural here. French typically uses the preposition à for participating in sports, games, and disciplines. Dans le karaté would sound like you are talking about being physically inside the sport.