Onto-On-To | Commonly Confused Words

Onto

/ˈɒntə/

Used to indicate movement toward a surface or awareness of something.

So he grabbed onto Don Quixote's trouser belt with both hands.The gate opens onto the moor.I pretend it doesn't sting as we step onto the train.

This word has no antonyms

/ˈɒn tu/

To be continuing towards a further stage or step

She's moved on to a new stage in her career.We'll get on to the next item on the agenda.He held on to her hand tightly.

Onto is a single word and it implies movement towards a surface or position on something else.
On to is formed by the preposition on followed by the preposition to and implies movement toward a point or destination that is often described in the sentence.
To remember: If you can replace it with upon without changing the meaning, you should use onto.
If separating them makes sense in the sentence structure, consider using on to.
Think of onto as a physical action of reaching a surface, while on to indicates progression or transition towards the next step.