When WordPress was first launched, it was specifically a blog. In fact when you first install WordPress now, the home page still defaults to showing the latest posts. Over time though, WordPress developed into a complete Content Management System (CMS) allowing users to create complex websites.
When you first log in, you’ll see menu entries for Posts and Pages.
Posts can be seen as news or updates. They are time specific in so far as they have a published date and are presented in archive pages in reverse order. Posts can be placed within one or more categories and also have tags applied to them, both intended to help readers find content.
Pages are static articles that are not time specific. These are intended to let site owners create websites with a more complex structure than a blog. For example, you may use pages to add a home page or contact page. Pages can have a hierarchy so that a parent page can have sub-pages and sub-pages can have their own sub-pages.
Comments allow readers to post feedback on posts and pages. By default comments are turned off on pages even if comments are enabled on the site as a whole.
Media is managed in the Media Library. Media covers images, videos, audio and several other file types such as PDFs and documents.
Plugins can be added through the plugins page and they add new features to WordPress. A plugin can be a very simple little thing, perhaps doing something as basic as changing the logo on the admin login page. At the other end of the scale, they can turn WordPress into a completely new type of site such as an ecommerce or real estate website.
Themes make it easy for anyone to change the appearance of a WordPress site without needing to know any kind of coding.
WordPress is an open source project and because of the way it is licensed, all themes and plugins that work with WordPress also have to be open source. Many plugins and themes are available for free, though there are also many commercial premium plugins and themes. In the case of commercial plugins and themes, you are usually paying for ongoing support and updates. So it possible and completely legal to acquire and use a premium plugin or theme without paying the author. However, you won’t be eligible for support or updates.
If you do acquire a premium plugin or theme from an alternative source, be aware that in some cases criminal groups can change the code to introduce a back door to sites, allowing them to take control. You should consider the risks very carefully before installing plugins and themes from non-official sources.