Joomla has both Front End & Back End components but the real question here is what is a component?
A component is an application within the Joomla framework some examples are the Joomla article system “com_content”, banners, menus, polls, links and contacts.
Some components are rendered in your Front End template as content for example articles. Others are used in the backend to manage things like user accounts.
A good question is How Do Components get called and render in the Front End template?
Believe it or not with just one tag.
<jdoc:include type="component" />
You can think of it as a main body tag in the center of your template.
Joomla then renders the content in your template based on the type of link past to it.
<jdoc:include type="message" />
this code for displaying the error messages to the user it’s very important and we can type it as:
<jdoc:include type="message" /> <jdoc:include type="component" />