You use code for that. The buttons at the top will provide the basic. If you want to just do a simple link you cut and paste the URL Example: You are not allowed to view links.
Register or
Login and the post will automatically code for you.
If you want to fancy it up you take that code [ url = http:// boards.straightdope.com/sdmb/misc.php?do=bbcode] http:// boards.straightdope.com/sdmb/misc.php?do=bbcode [ / url ] Remove the what is outside the [ ] and between the url= and the /url and put in what you want. For example it becomes:
You are not allowed to view links.
Register or
Login And looks like this: [ ur l= http:// boards.straightdope.com/sdmb/misc.php?do=bbcode] BB Code List [ / url]
Note I inserted spaces where there are suppose to be none to you could see what I did. If I had not done this, it would convert it into links and all you would see is the blue link.
The link I used will take you to a site that explains more about the code.