Learn Spanish (Latin America): Mi padre quiere mejorar su español.

In Spanish, when you want to say you want to do something, you conjugate the first verb (querer) to match the person, and leave the action they want to do in its basic dictionary form (the infinitive). Here, quiere means "he wants" and mejorar is the infinitive meaning "to improve".

I know the verb "to want" is querer. Why does it change to quiere here?

querer is a stem-changing verb. This means a vowel in the middle of the root word changes when you conjugate it for most subjects. The e changes to ie, which is why "he wants" (referring to mi padre) becomes quiere instead of "quere".

Why isn't the word español capitalized?

Unlike in English, Spanish does not capitalize the names of languages, days of the week, or nationalities unless they are the very first word in a sentence. So, "his Spanish" is written as su español with a lowercase e.

How do I know su means "his" in this sentence?