HTML documents consists of multiple element structure which includes start tag, attribute, body element, end tag etc.
The main tag of HTML is <html> and </html> which is start tag and end tag.
The content element is written between two tags i.e. body tag.
Few HTML elements have no body i.e. <br> tag which do not require to close tag.
Read Also: Meta Tags in HTML
An attribute can be added to HTML element.
<div id="one" style="background-color:#333333">...</div>
You can add tag inside another tag i.e. called nested element.
<div id="one" style="background-color:#333333"> <span>Hi there...</span> </div>
These are the basic building blocks that you will find yourself using on any web page.