On

 What is "On"?

On concerns place, movement, means of travel, or time.

1. On for "place"

1.1. On means "in contact with a surface" or "touching"

1. There's a fly on the ceiling.
2. The TV is on the table.
3. There's a clock on the wall.
4. The ship is on the sea. (Essential English Book 1 at page 12)

Please notice that on frequently means "on top of":
Ex: A cat is on a box.