Inline Elements apply formatting inline with the flow of text. The following formatting is all done with inline HTML elements (also called text elements): bold text (b), italic text (i), small text (small), highlighted text (mark), monospace font (code), superscripts (e=mc²), and subscripts (H₂0). Inline elements can even be applied inside words. That looks strange in the HTML code, but the browser replaces the HTML tags with the formatting they induce.

Block Elements carve a block out of the web page. This text is inside a paragraph (p) block as you can see in the HTML source code.

This text is inside another paragraph block. Notice in the web page that there is a blank line between this paragraph and the previous one. It makes sense that consecutive paragraphs should automatically be separated by a blank line.

The line below is created with a horizontal rule (hr).

A horizontal rule is kind of like a line break, but makes a horizontal divider in the page.

The blocks below are all created using Heading Elements: h1, h2, h3, h4, h5, h6. They are used to create sections, subsections, sub-subsections, etc. There are only 6 levels of headings, all of which automatically apply boldface.

Heading level 1

Heading level 2

Heading level 3

Heading level 4

Heading level 5

Heading level 6

This is a blockquote which is basically just a paragraph with extra left and right margins. This is intended to be used to create indented quotations.

This is a pre-formatted block (pre) - preserves whitespace and induces a monospace font (e.g. monaco or courier). 

In the Land of Mordor where the Shadows lie.
    One Ring to rule them all, One Ring to find them,
    One Ring to bring them all and in the darkness
       bind them.
In the Land of Mordor where the Shadows Lie.