Learn Russian: Дорога длинная.

In Russian, the present tense of the verb "to be" (am, is, are) is almost always left out. So, Дорога длинная literally means "Road long," but it naturally translates to "The road is long."

Why does the adjective длинная end in -ая?

Russian adjectives must match the gender of the noun they describe. The noun дорога (road) is feminine because it ends in -а. To match it, the dictionary form of the adjective (длинный) changes its ending to the feminine -ая.

How do we know it means "The road" and not "A road"?

Russian doesn't have articles like "a" or "the." You have to figure out which one makes sense based on the context. Since this sentence is describing a specific road's length, "The road" is the most natural English translation.

Why are there two н's in the middle of длинная?

This happens when an adjective is built from a noun that already contains an н. The root word for length (длина) has one н, and the adjective suffix adds another -н- before the ending, resulting in the double нн.