'Into' is a combination of 'in' and 'to'. It combines the location of 'in' with the movement of 'to'. Compare these pairs of sentences: The teacher is in the classroom. The teacher walked into the classroom. The pizza is in the oven. I'll put the pizza into the oven. I think that's clear - 'into' is for a movement. The confusing thing is that we can often replace 'into' with 'in'. For example, it's possible to say 'I'll put the pizza in the oven'. This is correct and normal. We don't always have to use 'into' - in many cases, 'in' is fine, and the movement is understood. However, we can't use 'into' if there is no movement. For example, you cannot say 'The teacher is into the classroom' or 'The pizza is into the oven'. These sentences make no sense. If there is no movement, you have to use 'in'. If there is movement, you can use either 'into' or 'in'. So, if in doubt, use 'in'! By the way, the same goes for 'on' and 'onto'. So you can say: The pizza is on the table. I'll put the pizza onto the table/ I'll put the pizza on the table. I hope that helps.