h1-6 Tags
These tags are header tags. They accept the align(right, center, left) modifier. h1 is the biggest, and h6 is the smallest. Also, header tags have a built in line break before and after them. (All of the 'titles' on this page are examples of them). Example: <h3 align="right">Header!</h3>.
b and i Tags
These are the bold and italics tags. They have no modifiers - they simply bold or italicize the text that they enclose. Be sure to close these! You'll get a big surprise when you open the page if you don't!
br Tag
Also a modifierless tag. It is simply a line break. You may have noticed that the browser doesn't display any line breaks that you put into the code. You have to explicitly insert one into the code with this tag in order for it to appear on the page. Example:<br>.
pre Tag
This tag formats the text that you put in between it exactly as it appears in the code. The browser ignores pretty much all of the whitespace you put in the code - it doesn't ignore it if it's in this tag. It displays all line breaks, too. It also gives the text a typrewriter font. Remember to close this tag too! This one also has built in line breaks before and after it. Ex: <pre> and </pre>.
tt Tag
This gives the text that it encloses a typrewriter font like the pre tag without the formatting and built-in-line-break part. Ex:<tt>Typrewriter font!</tt>.
blockquote tag
This is a neat little tag. It puts a few line breaks above and below the block of text it contains, and increases the left and right margins.
<blockquote>Basically it looks like this. Make the window really small until it wraps this text to the next line to see the right margin.</blockquote>