Here's how to tell:
* Preposition: When "into" connects a noun or pronoun to another word in the sentence, it's a preposition.
* Example: "The ball rolled into the goal." (Here, "into" connects the noun "goal" to the verb "rolled").
* Adverb: When "into" modifies a verb or adjective, it's an adverb.
* Example: "He looked into the distance." (Here, "into" modifies the verb "looked").
It's not a verb, noun, or adjective on its own.