Learn Russian: Парк — два километра.

This is exactly what your current lesson covers! After the numbers 2, 3, and 4, Russian nouns change into the Genitive singular form. The dictionary form is километр, and its Genitive singular form is километра.

Why do we use два and not две for the number two?

In Russian, the number two changes depending on the gender of the noun it counts. We use два for masculine and neuter nouns, and две for feminine nouns. Because километр ends in a consonant, it is a masculine noun, so it takes два.

Why is there a dash between Парк and два?

The dash acts like the English word "is". Russian usually drops the present tense of the verb "to be" (am, is, are). When linking a subject (Парк) directly to a noun or a number describing it, written Russian often uses a dash to stand in for the missing verb.

Where is the word for "away" in the Russian sentence?

There isn't one, because Russian doesn't need it here! The literal translation is "Park — two kilometers." In Russian, simply stating a place and a distance implies that it is that distance away from your current location.