These words are mostly used to show a thing’s position or object.
In
When something is located in a defined place. It could be a flat place like a yard, house, or park. The thing should not be covered from each side. The below picture is an example of the use “in”
Example: The teacher is sitting in the chair.
Inside
When something or object is located in a place covered from every side and has an upper side we use inside. The below-mentioned picture also indicates the use of inside.
Example: Parrot is sitting inside the cage.
Into
When something is moving from the outside to inside the object.
Example: He is pouring water into the glass.