When I add a template to my webpage, do I have do everything over again, like adding the services and what I have written in the webpage, or does it just change the webpages's look?

A template is a web page that hasn't had the content added yet. You normally add your content to the template not the template to your content.

Most of the time it is easier to cut your content from the old template and paste it into the new one rather than trying to replace the template in the existing page.