The difference between in and into is whether or not there is movement. Into is used when something or someone is going or being put into another location. In is used to describe where someone or something already is.
Ex: She is in the room. She walked into the room.
The toy is in the box. The boy put the toy into the box.
In American English, we sometimes use the two prepositions interchangeably. Ex: She got in the car. She got into the car. Both are acceptable.