This is easy to do in the Twenty Ten theme, where pages are typically used as the basis for your navigation menu. Instead of adding a page, you can add the URL to your category slug.
- Find the category URL by simply clicking on the link to that category. For example, on this site the category “web diy” is:
- In your admin panel, click Appearance > Menus.
- Under Custom Links, paste the URL for the category you want to add.
- In the Label field, type a title for the menu item. This is what will appear in the menu itself.
- Click Add to Menu.
- Click Save Menu.
Tip: You can use a custom naming convention in your category URLs by going to Settings > Permalinks, and editing the option Category base field. (Warning – this will change the URL of your existing categories, thereby breaking any links to them that may be out there, so proceed with caution.)