How to Set a Minimum Word Count for WordPress Posts with or without plugin
Have you googled that question? I just did, and came up with quite a few articles that deal with that issue. For example:
and many more.
A great way to learn in web development is to practice hunting for answers on Google, and being able to determine whether the published source is reliable.
Try this, and if you have any questions about what you find, please feel free to ask here.