Caption is a word with two main meanings:
* A short explanation or title accompanying an image, video, or other media. This is the most common use of the word. For example, a caption under a photo might say "My family at the beach."
* The act of writing a caption. For example, "She captioned the photo with a funny quote."
Capit is not a word in the English language. It's possible you've heard a word that sounds similar, such as "capitol," which refers to a building where a legislature meets, or "capital," which can refer to a city, money, or a letter in uppercase.
Let me know if you have any more questions or if you meant something else!