Theme: Theme is the “look and feels” of an online blog, like the colored background, header graphics, font styles, and text styles.
A theme in WordPress is what you see when you load your domain name in your browser. Themes define all aspects of site appearance such as colors for backgrounds or page elements to which fonts will be used for headings or body text. A WordPress theme can also be a plugin that dynamically changes the look and feel of parts of your website after generating it with a layout engine like Bootstrap.
Plugins: A plugin in WordPress is an external code that can modify/enhance the core functionalities of your website. Plugins range from being simple one-line adjustments to more robust, complex modifications, and exist for all sorts of uses, including making it easier to perform routine tasks or providing visual tools for online marketers.
Configuring plugins for your site is as easy as clicking on “add new” and searching the list until you find the desired function. Once installed, they will show up in a box on the left of your screen titled “Plugins”. If you click on any one of these plugins, a description will appear below it with links to edit every feature associated with that plugin–so be sure before adding each one.