Learn Hardcore Hindi: हम पार्क में चलेंगे।

हम = ham, not exactly English hum, but close.
पार्क is a borrowing from English park, usually pronounced pretty similarly.
में is often written mein in learner-style transliteration; the vowel is nasalized.
चलेंगे has a -enge sound at the end: cha-len-ge.

What does each word in the sentence do?

Here is the breakdown:

So the structure is basically:

we + park + in + will walk

Why is it पार्क में and not में पार्क?

Because Hindi uses postpositions, not prepositions.

In English, words like in, on, and at usually come before the noun: