on + object

on = on a surface.

For example,

  • There’s a clock on the wall.
  • What’s that on the ceiling?
  • There’s a bag on the floor.
  • My books are on the table.

on = not exact address.

For example, I live on Oxford Street. (However, for an exact address, you say “I live at 55 Oxford Street.")

on = attached to.

For example, She is wearing a ring on her finger.

on = close to a river.

For example,

  • London is on the River Thames.
  • My house is on the River Avon.