Here are some ways to use it:
* Dit-on que le roi est malade? (Does one say that the king is sick?)
* Dit-on qu'il va pleuvoir? (Does one say that it is going to rain?)
* On dit qu'elle est partie. (One says that she left.)
It can also be used as a synonym for "it is said" or "people say."
Keep in mind that "dit on" doesn't necessarily mean the information is true. It simply indicates that it is being discussed or reported by others.