"into" is a preposition used as a function word:
1 - to indicate entry, introduction, insertion, superposition, or inclusion
Example: I came into the house.
2 - to the state, condition, or form of
Example: She got into trouble.
3 - to the occupation, action, possession of, involved with, or interested in
Example: I will go into farming.
4 - to indicate a period of time or an extent of space part of which is passed or occupied
Example: I took far into the night.
5 - in the direction of
Example: She was looking into the sun.
6 - to a position of contact with; against
Example: The car ran into a wall.
However, "into" cannot be used for "in to"!
Example:
She turned her paper into her teacher. (INCORRECT)
She turned her paper in to her teacher. (CORRECT)
See the following partitioning to understand why:
She turned ... in.
She turned her paper in.
To her teacher.
"She turned her paper in" + "To her teacher"
She turned her paper in to her teacher.
