Container Tags come in corresponding opening and closing tag pairs.
These tag pairs work together to mark off blocks within the HTML document.
A block being the region of the document between such corresponding tags.
Symmetry between opening and closing tags must be maintained throughout an HTML document.
I.e. between any opening and closing tag pair, all other tag pairs opened must be closed.
The effect of a container tag pair is applied to the block it marks off.
When a section of text is contained within multiple tags each tag applies its effect to the text.
Container tags are applied in order from most outer to most inner, so that if two tags effect the same aspect of a section of text it is the effect of the most local tag that applies. Non-container Tags are singelton tags, they do not have corresponding closing tags.
Their effect is applied at the point in the HTML document where they appear. Each version of HTML defines an available set of tag types and their default behaviors.
Use of an undefined tag type causes a tag to be ignored in the interpretation. Each instance of a tag has multiple attributes all of which have default values.
Some attributes can be set to non-default values specified by the webpage designer.
Modifying the attributes of a tag from their default values modifies the tag's behavior. If it's a container tag its effect is applied to the block between opening and closing tags.
If it's a non-container tag its effect is applied at the point at which the tag appears. All tags begin with an opening angle bracket, i.e. < . One of the tag types defined by the version of HTML being used goes here.
There must be no whitespace immeadiately prior to the tag type.
If there is preceeding whitespace then the source code will not be interpreted as a tag.
There must be whitespace immediately following the tag type.
If not the tag will be interpreted as the wrong tag type. A slash follows the opening angle braket of a closing container tag.
It is this slash that distinguishes the tag as a closing tag, as the tag type will match with an opening tag.
There can be no whitespace either before or after this slash. An optional whitespace seperated list of attribute value pairs may appear here.
The atribute list must be seperated from the tag type by whitespace.
The specific attributes that can be set depend upon the tag type as well as the version of HTML. All tags end with a closing angle bracket, i.e. > . One of a large number of attributes dependant upon the tag type. Almost all attributes are set to new values using an equal sign, i.e. = . Possible values depend upon the particular attribute being adjusted.

Tags

Syntax - Opening Container Tags & Non-container Tags:

Syntax - Closing Container Tags:

Syntax - Attribute Value Pairs