Meaning of “onto” - Learner’s Dictionary

onto

preposition ( also on to) uk us /ˈɒntuː/
MOVING

B1 used to show movement into or on a particular place:

The sheep were loaded onto trucks.
Can you get back onto the path?
hold/grip, etc onto sth

to hold something:

Hold onto my hand before we cross the road.
TALKING

B2 used to show that you are starting to talk about a different subject:

Can we move onto the next item on the agenda?
be onto sb

to know that someone has done something wrong or illegal:

She knows we're onto her and she's trying to get away.
Who put the police onto (= told the police about) her?
be onto sth

to know or discover something useful or important:

Researchers think they may be onto something big.
Can you put me onto (= tell me about) a good dentist?

(Definition of “onto” from the Cambridge Learner’s Dictionary © Cambridge University Press)