To link from elsewhere, say google, copy or cut the url and then click POST REPLY in the thread you want to place it, and then go to the URL box and that will open a little window where you can put the link (making sure you only have one
http:// when you've done, and enter that. Another window comes up, and you give the link a name.
This procedure keeps the links from being so long that they stretch out the thread's page so wide that it doesn't fit the screen.
Only other warning is don't post a personal website as it is against A2k's Terms of Service as being a kind of spam.