Here's an example:
* Happy people smile more often. (Happy describes the people)
However, you can sometimes use "happy" as a noun, but it's less common.
Here are some examples:
* The happiest of all was my little brother. (Here, "happiest" is acting as a noun, meaning "the one who is happiest")
* We were all in a state of happy. (Here, "happy" is used as a noun to refer to a state of happiness)
It's important to remember that these examples are a bit informal and uncommon. In most cases, "happy" will be used as an adjective.