The paragraph <P> tag defines a paragraph of text.

The horizontal rule <HR> tag places a line across the page. So it's a visual feature.

This is emphasised text.

Most browsers display emphasised text in italics so I could have used an Italics <I> tag to get the same effect, but italics are meaningless to non-visual browsers.

This is strongly emphasised text.

Most visual browsers display strong text in bold font so I could have used a Bold <B> tag, but that is also meaningless to non visual browsers.

The Tele-Type <TT> tag tells visual browsers to use a fixed-width (typewriter) font

The Center <CENTER> tag centres the text on the page. Note that it is a visual feature so has no meaning in a non-visual browser; it tells us something about the appearance of the information, but nothing about the meaning of the information. Don't forget that the center tag has to be spelt the American way.
Many web authors use the Blockquote <BLOCKQUOTE> tag to indent text. However, not only should they not be indenting text (what does indented text mean to a non-visual browser?), but they are giving a false meaning to the text, even in visual browsers. They may be giving the impression that the text in between the tags is actually a quote, which it is (probably) not.

The Break <BR> tag is used to create a line-break within a page.
This sentence should appear below the previous sentence since a Break tag appears between them. This is not a meaningful tag, but it is sometimes necessary for visual browsers to keep a tidy appearance.

The heading <H?> tag tells the browser about the meaning of it's contents, but it conveys nothing about the presentation of the content. This way, each user can configure their browser to present the content in the way that best suits them.

This text appears within the Heading 1 <H1> tag

This text appears within the Heading 2 <H2> tag

This text appears within the Heading 3 <H3> tag

The <UL> tag defines an Unordered List (un-numbered, or bulletted). The idividual items in the list are defined with the List Item <LI> tag.

The <OL> tag defines an Ordered List (numbered).

  1. This
  2. Is
  3. An
  4. Ordered
  5. List

We use the Definition List <DT> tag for creating a glossary ( a list of definitions).

The Definition Term <DT> tag surrounds the term to be defined.
The Definition Definition <DD> tag surrounds the definition of the term.
Computer
A versatile box of sand and copper

A Table is created using four main tags. The Table <TABLE> tag defines the overall table. The Table Row <TR> tag defines a table row. Within each row, the Table Data <TD> tag defines each cell (a column within a row). The Table Header <TH> tag defines the headings for each column and is used in the first row of the table.

Column 1 Header/Label Column 2 Label Column 3 Label
Cell 1,1 Cell 1,2 Cell 1,3
Cell 2,1 Cell 2,2 Cell 2,3 

This is a scrap of text that uses the Pre-format <PRE> tag.
The browser displays the text exactly as it appears with all spaces and line-breaks intact.
So  this   line   should have   lots   of  spaces   between   words.

To make a hypertext link, we use the Anchor <A> tag. The part in the quotes section of the A HREF="" is the URL for the page we are linking to. While the part between the A HREF tag and the /A tag is the text that appears as the link in the browser.

This is a relative link to this document.

We use the Image <IMG> tag to include an image:A small piece of text to explain this image to non-visual browsers