on, on to, onto

The preposition on expresses the location of a person or an object relative to another.

• Henriette sat calmly on the waiting-room sofa.
• The travel budget should be on the agenda for the February meeting.

Onto expresses movement.

• As soon as Allan left the room, the kitten jumped onto the table.

The words on and to remain separate if a change of position does not occur, especially with phrasal verbs such as catch on and go on.

• Has the dog caught on to your trick yet?
• It is time to go on to the next stage of the project.