As you make your Joomla! site you will control the details of the display using options also referred to as parameters. Options control everything from whether the authors name is displayed to who can view what to the number of items shown on a list.
Default options for each component are changed using the Options button on the component toolbar.
Options can also be set on an individual item, such as an article or contact and in menu links.
If you are happy with how your site looks, it is fine to leave all of the options set to the defaults that were created when your site was installed. As you become more experienced with Joomla you will use options more.