The preposition in generally refers to being inside something: Adam stood alone in the elevator. While the preposition into generally means movement toward the inside of something: Adam walked into the elevator.

But sometimes the meanings of in and into sometimes overlap.

Examples:

  • After waiting in the hallway for twenty minutes, I finally stepped into the manager’s office.
  • On her way back from Damaturu, Ladi ran into a snowstorm and took a wrong turn in Fokka.
  • The number-one way of getting your parents’ attention is getting into trouble in school.
  • Not only is there a distinct symbolism in the designs woven into the basket, but in some cases the basket itself is a symbol.

Generally, in and on are used to talk about the positions of things–where they are; and into and onto to talk about directions and destinations–where things are going.

Compare:-

A moment later the ball was in in the goal.

The ball rolled slowly into the goal.

She’s in the bedroom getting dressed.

She ran into the room carrying a paper. 

She was walking in the garden.

Then she walked into the house.

The cat’s on the roof.

How does it get onto the roof

Note that into and onto are normally written as single words. On to is also possible in British English, as in: I am on to you.

The combination of the verb turn with in plus to and with into can create a problem: A man can turn himself in to the police, but, unless he’s a magician, he can’t turn himself into a rabbit.

See the difference? The spelling in this instance reflects a difference in intonation, as in to sounds quite different from into.

Into is also current slang, meaning interested in, excited about, or knowledgeable about, as in: Tola is really into that boy that just changed school

Difference Between Into and In To

Most of the time the choice between these is straightforward. Compare:

They went into the theatre.
They went in to the reception.

The spaced form ensures that in as used in the second example is interpreted in relation to the verb, went, and adds a detail of movement that would otherwise be lost had it been removed. But in practice, into is quite often used where in to might be justified, without too much being lost.

From about.com

See Also: PREPOSITIONS: Is It Wrong to End Sentences With Them?