Tag Structure:
The structures that describe parts of an HTML document are called "Elements" or "Tags", and consist of 4 parts: the start tag, the tag attribute, the content, and the closing tag.
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Tag Brackets:
Tags are enclosed between and open and close brackets such as these: <  >. An example is the start tag to make text bold. The bold tag is written as <B> .
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Tag Attribute:
This defines various properties for a given tag and is included in the start tag only and never in the closing tag . An example is image tag: <IMG> which has a number of attributes such as the SRC (image location), WIDTH, and HEIGHT. Attribute names are case-insensitive, but attribute values may be case-sensitive. "The attribute value is delimited by single or double quotes. The quotes are optional if the attribute value consists solely of letters in the range A-Z and a-z, digits 0-9, hyphens, and periods ( . )." Example:
   <IMG SRC="mypicture.gif" Width="100" HEIGHT "60">
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Content:
This is where you would place your content for a particular tag. It can be text or an image for your page.
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Closing Tag:
To close a tag, you add the slash / to the tag. A closing tag would looks like this: </B>. With the content added, the example would be written as:

<B>This is Bold text.</B>   It would look this this: This is Bold text.

It is important to remember to always close your tags. Even though some web browsers (such as MS Internet Explorer) can display a webpage that contains missing closed tag errors, your page will not display correctly in Netscape. Tables are especially vulnerable to missing closed tags.

Some tags do not require a close tag because they contain no content. An example of this is the "Break" tag: <BR>
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Case Sensitivity?:
Element names are NOT case sensitive, so <em>, <eM>, and <EM> are all the same.

Beware, file names ARE case sensitive, so <img src="mypicture.jpg"> is NOT the same as: <img src="mypicture.JPG">
or the same as: <img src="MyPicture.jpg">
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Nesting:
Tags sometimes contain other tags inside a section of content. Tag pairs should be nested within one another and their end tags should not cross. For example, to make a section of text bold and italic, the correct way to write this would be:
    correct   -  <B><I>This is bold and italic.</I></B>
and not this:
    incorrect -  <B><I>This is bold and italic.</B></I>
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Extra Spaces and Unknown Elements:
Browsers will collapse and ignore space characters in the HTML content. Extra spaces, tabs, and carriage returns are ignored and are not displayed unless they occur inside the <PRE>     </PRE> tag.

Browsers also ignore unknown elements and unknown attributes in a document. For example:
  <MOVIE>Toy Story</MOVIE> is not an HTML tag, but will render "Toy Story" as regular text.
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