There are two ways to make internal links from one content page to another in WordPress. One uses permalinks and one does not. If you are not using Permalinks, how do you link to your pages, posts, and categories?

Using the numeric values found in the ID column of the Posts, Categories, and Pages Administration, you can create links as follows.


Posts

To link to a Post, find the ID of the target post on the Posts administration panel, and insert it in place of the '123' in this link:

<a href="index.php?p=123">Post Title</a>

Categories

To link to a Category, find the ID of the target Category on the Categories administration panel, and insert it in place of the '7' in this link:

<a href="index.php?cat=7">Category Title</a>

Pages

To link to a Page, find the ID of the target Page on the Pages administration panel, and insert it in place of the '42' in this link:

<a href="index.php?page_id=42">Page title</a>

http://codex.wordpress.org/Linking_Posts_Pages_and_Categories