an adverb is a part of speech that modifies the meaning of adjectives, verbs, or other adverbs. An adverb usually refers to the time, manner, place or degree in which a verb is expressed. 'Soon' is an adverb that suggests 'in a short amount of time.' Here are some example uses
He should arrive soon.
She wants to leave soon.
We'll be happy to help you soon.
when using 'soon' as an adverb, the amount of time referenced is usually pretty short. However, the exact amount is often left open to interpretation. Usually, 'soon' implies either 'immediately' or 'in the near future.' Be sure to clarify the exact meaning if you need to be more specific.