From YPPedia
Find the article you want to apply the template to, and Edit it.
Identify the template you want to apply to the page, and note the article name.
Convert the article name into a template caller, by removing "Template:" and adding a pair of curly brackets on both ends.
Add the template caller to the appropiate place in the article.
Save the page, and make sure it's applied itself properly. Pat yourself on the back and bask in your awesomeness.
Examples of "Simple" Templates
Simple templates are templates that don't require additional information or input to be used.