As you make your Joomla!® site you will control the details of the display using options also referred to as parameters.
Options (parameters) control everything from whether the author's 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, contact, and in menu links.
If you are happy with how your site looks, it is fine to leave all of the options (parameters) set to the defaults that were created when your site was installed.
Certainly - as you become more experienced with Joomla you will use options more.
Your Joomla!® website comprises Options for various features (for want of a better word), such as:
- Blog/featured layouts;
- List layouts.
Each of those have "Options".
The options will have default settings which will be perfectly adequate for starting your website development. When, for example you create articles - those articles will inherit the default options for articles.
If you wish for any specific article, or articles, to have different settings you can change those settings on an article by article basis.
The same applies to categories, list layout, or blog/featured list layout - the options can be changed on a case by case basis.
For a more explicit example: the default article option for "Show category" is set to Hide (in "Article --> options"). When any article is visited on the frontend its Category is NOT shown.
For your article, lets call it "abc", you want its category to be shown, open up that article in the Administrator area and you can set "Show Category" option to under the specific article's Option tab) to: "Show". Article abc will show its category when visited on your website frontend.
If you want ALL articles to have the category shown on your website frontend - simply go to Articles --> options, and set "Show category" to: "Show". When you create a new article hereafter it will automatically show its Category because, by your newly set default, the article specific option to Show Category will be set to "Use global".
A more visual presentation may be shown here in the Joomla!® documentation on Article Manager Options.