The Navigation popups gadget allows easier access to several Wikipedia features as "popups" which appear when you hover the mouse over links. With this useful tool, when you hover your mouse cursor over a wikilink you can see a preview of the article or image; plus you can activate convenient functions such as going directly to the talk, edit, or history pages.
To use the navigation popups gadget you must be logged in under your own user account and turn on the gadget in your Preferences, available at the top right of your screen. In your preferences you will find navigation popups under Gadgets, Browsing gadgets. Full instructions are on the Navigation popups page.
To add a link to a category in an article (as opposed to adding the article to a category) create a normal link to the category page but place a colon at the beginning of it, just after the double opening square brackets. Here's an example:
To provide a link to Category:Animals (just like this one), add the text [[:Category:Animals]] where you want the link to appear. (Notice the extra colon at the beginning of the link).