<html> tag is the root element and defines the whole HTML document.
HTML tags can be nested i.e tags can contain other tags.
HTML tag is Not Case Sensitive i.e <P> means the same as <p>.
Never skip the closing tag else one will get unexpected results.
HTML tags with no content and closing tags are called Empty Tags Eg: <br>, <hr>, <img>, <input>, <meta> etc
Other commonly used tags are: <div>, <p>, <a>, <ol>, <li>, <footer>, <header>, <nav>, <section>, <pre>, <code>, <form>, <em>, <strong> etc.