Into: preposition; expresses movement of something toward or inside something else.
I made it into work a few minutes early today.
I tucked my mittens into my pocket.
In to: adverb in followed by the preposition to.
The principal sat in to evaluate the new teacher.
The tooth fairy came in to collect Betsy’s tooth.
Here’s a way to remember:
Into usually answers the question “where?” while in to can be replaced with “in order to.”