As a noun:
* He climbed the ladder, carefully moving from one rung to the next. (This refers to a step on a ladder.)
* The social ladder has many rungs, each representing a different level of wealth and status. (This uses "rung" metaphorically to describe levels of society.)
* She had reached the top rung of her career. (This also uses "rung" metaphorically to describe a position of success.)
As a verb (past tense):
* He rung the doorbell twice before anyone answered. (This means "to cause a bell to sound by pulling on a cord or lever").
Let me know if you want to see more examples!