* He swears he didn't break the vase, but I saw him do it! (meaning: He claims to be innocent, but I know he's lying)
* She swears off coffee for a month to see if it improves her sleep. (meaning: She promises to stop drinking coffee for a period of time)
* The witness swears that he saw the suspect flee the scene. (meaning: The witness gives a strong, confident statement)
* The old pirate swears by the power of the sea. (meaning: He believes strongly in the power of the sea)
* She swears like a sailor when she's angry. (meaning: She uses a lot of strong language when she's upset)
The meaning of "swears" can change depending on the context. It can express strong belief, a promise, or even a habit of using profanity.