The Caps key on a keyboard is used to switch between upper and lower case letters.
When you press the Caps key, it changes the letter case of the letters you type from lowercase to uppercase or vice versa. This means that if you type with the Caps key on, all the letters you type will appear in uppercase. Similarly, if you type with the Caps key off, all the letters you type will appear in lowercase.
This feature is particularly useful when you want to emphasize certain words or phrases, such as in titles or headings. It can also be used to make your text easier to read by adding some variety to the letter case. For example, when typing a password or other sensitive information, you may want to use a combination of upper and lower case letters to make it more secure.
In summary, the Caps key is used to switch between uppercase and lowercase letters in order to make text easier to read, emphasize words, or add security to sensitive information.