As a noun (meaning a festive song):
* The children sang carols around the Christmas tree.
* We heard the sweet sound of carols echoing through the streets.
* The choir performed a beautiful selection of carols.
As a noun (meaning a person named Carol):
* Carol is coming to the party tonight.
* I met Carol at the library.
* Carol's birthday is next week.
As a verb (meaning to sing carols):
* We're going to carol in the town square tonight.
* The children were caroling door-to-door.
* We caroled joyfully through the streets.
Let me know if you'd like to see more examples!