Putting this template on a page marks it as a stub article, and puts it into Category:Article stubs.
You can optionally use one parameter with it. Adding a parameter puts the article into a category based on the parameter you used, instead of the default "Article stubs" category.. The category will be called "whatever stubs", where whatever is what you put in. For example, this:
...will result in the page being put into a category called "ritual stubs".
Don't forget to make a note of it in Category:Article stubs.