Tags are what I can best describe as the "words" used in the HTML language. An author uses these tags to control the placement and attributes of text and images within a page.
Most tags have an "opening" tag and a "closing" tag, E.G. <HTML> is the opening tag and </HTML> is the closing tag. As you can see the "/" means that it is a closing tag. This to tell the browser when to start to, say bold text and when to end bold text. If the closing tag was not there, the rest of the text after the opening tag would be bold.
There are some tags such as the line break tag <BR> and the Horizontal line (or rule) tag <HR> that do not need a closing tag. The <BR> tag works the same as the carriage return on a type writer or return on a computer keyboard. The <HR> tag create a line across the page like the one below.
While I'm on the subject of the <BR> tag, there is an important point to remember with HTML and browsers, in that they do not work in the same way as an ordinary typed document. A browser will read an HTML document and will ignore any "white space", EG. if you have six blank lines or carriage returns, the browser will ignore it and display text directly below or next to the previous text. To avoid this, the <BR> tag does the same as a carriage return.
Without <BR> tag..
Hello Hello HelloWith <BR> tag
Hello
Hello
Hello