Learn Hardcore Spanish (Spain): El niño quiere jugar en el parque.

In Spanish, el is the masculine definite article (meaning the). Since niño (boy) is a masculine noun, we use the masculine article el before it.

What tense is quiere, and why is it used here?

Quiere is the third-person singular present tense of the verb querer (to want). It's used because we're describing what the boy wants to do right now (to play in the park).

Why is the infinitive jugar used after quiere?

In Spanish, when you want to say someone wants to do something, you use the verb querer followed by an infinitive. That's why querer + jugar (to want + to play) is the correct construction.

What does en el parque translate to, and could we use al parque instead?

En el parque translates to in the park or at the park in English. You might see al parque if you're talking about going to the park (for example, ir al parque). In this sentence, en is used to indicate location (where he wants to play).