As the name suggests, Functions add functionality to your WordPress page. These Functions can either be coded directly into your theme, which is why every theme seems different, or they can be used in a Plugins using ‘hooks’ that hook into the source code of WordPress to do various things. Check out some of the things that WordPress Functions can do.
get_sidebar – This Function adds the sidebar to your theme. Without it, you wouldn’t have one.
get_header – Adds a header area to your theme. Would you want this if your Pattern has one?