1) The basic link:
<a href="url">Text to be displayed</a>

url the address of the page you want to link to, like http://www.blahblah...
Text to be displayed write some text to serve as a link, like GO HERE or Enter my Dungeons!

2) The basic link which will open in a new browser window:
<a href="url" target="_blank">Text to be displayed</a>

adding target="_blank" after your url will open the link in a new browser window. It can be used in LJ, IJ etc and places other than LJ, IJ etc. Some fanfiction archives allow for use of html links in your profile (make sure that a window you are pasting your html into is not in "rich text mode", switch to html mode first)
Target has many more uses (like target="_top" , but I never used this one:)

3) The basic link with text appearing when the cursor hovers over the Text to be displayed:
<a href="url" title="text">Text to be displayed</a>
<a href="url" target="_blank" title="text">Text to be displayed</a>

Examples for 1) 2) 3) which all lead to my other comm:
1) Go to hp_polls

2) Go to hp_polls

3) Go to hp_polls

Go to hp_polls