What are HTML Tags?
First, HTML is short for "HyperText Markup Language". That means it is a programming language for prettying up and ordering text documents.
So, lets define the word "tags":
html tags, written by a person, are deciphered by a web browser, where the tag defines what the browser is to display on the screen, and how it is to be displayed.
Most tags must have two parts, an opening and a closing part. For example, <html> is the opening tag and </html> is the closing tag. Note that the closing tag has the same text as the opening tag, but has an additional forward-slash ( / ) character. I tend to interperet this as the "end" or "close" character.
There are some tags that are an expections to this rule, where a closing tag is not required. The <img> tag is one example of a tag which does not have a closing tag.
The HTML document
Simply put, each web page is just a text document, and is made up of many HTML tags. We therefore call them HTML documents.
Each HTML document must have the essential tags for it to be valid, which are explained here
Tag Attributes
Attributes allow you to customize the tag, and are defined within the opening tag, for example:
<img src="image1.jpg"> or <p align="center"> ... </p>
Most attributes for most tags are optional, however, some tags such as the <img> tag has required attributes such as src and alt which are needed in order for the browser to display the web page properly.