Faraway is a single word used as an adjective to describe something that is distant or not nearby.
Far away is two words; it indicates a distance from something else and usually follows a verb.
If you can replace the word or phrase with distant, use faraway.
If the phrase follows a preposition and shows physical or metaphorical distance, use far away.
Remember: Faraway is frequently used in front of nouns as a qualifier, whereas far away often follows contexts requiring prepositions indicating distance.