These two prepositions have very different meanings and different rules for use. As is the case for many English grammar rules, however, there are exceptions. These exceptions are especially helpful for native English speakers to know, because they will recognize subtle differences in meaning.
Instructions
1. Know the rules. These prepositions are not interchangeable. "Into" has motion. "In" is a location or position.
2. Study these simple examples: The cook was in the kitchen (position, location). The restaurant owner walked into the kitchen (movement).
3. Understand, however, that "into" and "in" overlap. Look at these examples: He threw the trash in the barrel. He threw the trash into the barrel. These two sentences say the same thing. Here's another set: File your important papers in chronological order. File your important papers into chronological order. They mean the same.
4. See in these following examples how, in most cases, the rules do apply. The flowers are in the room. The flowers are into the room. She danced in the studio. She danced into the studio. The bird flew into the glass. The bird flew in the glass. "Into" and "in" mean have very different functions and meaning in these examples.
5. Note also that "into" is unacceptable by English experts as slang. It is weak, sloppy and ambiguous. In proper English, it is best not to use "into" as someone being into something. An example: She's into vegetarianism. Instead, say, "She's a vegetarian" or "She is interested in the health benefits of vegetarianism."
