1. Use the URL you see in your browser window for the post you want to link to. Its done no differently than anywhere else.

2.

Pretty url:

http://www.domain.com/category/mystuff/newstuff

Ugly url:

http://www.domain.com/index.php?p=1

.. or anything similar.

[wiki]permalink[/wiki]

andimac,

To expand a bit more on Whoo's help ...

1) Pretty URLs (typically) contain words that are more relevant to the post and avoid the use of "URL parameters". (They're more search engine friendly, as well as being easier to read)

2) Ugly URLs can contain a raft of URL parameters, separated by specially query string characters (?, & and =) and can get quite out-of-hand. (e.g. - from a windows server, which cannot "do" pretty, or clean, URLS: [url=http://astonishme.co.uk/portfolio.php?title=good_boating&more=1&c=1&tb=1&pb=1]http.//astonishme.co.uk/portfolio.php?title=good_boating&more=1&c=1&tb=1&pb=1[/url]).

Historically, search engines often tripped on all the special characters, though it's not as much of a problem now, because most engines can handle them.

3) Generally, when I want to add a link to a post, in my own blog, I'll right-click the permalink icon and "copy shortcut". I then insert it

<a href="here" title="blah">link to the post</a>

in an anchor tag.

Hope this helps.