As a general rule, 'in' and 'on' express position, and 'into' and 'onto' express movement.
Position: We were sitting IN the café. She stood ON the balcony.
Movement: We went INTO the café. She walked ONTO the balcony.
We sometimes use 'in' and 'on' for movement, especially in informal English:
We went in the café.
The opposite of 'into' is 'out of':
'She got out of the car and went into a shop.'