To create a link between cards you must have created at least two cards. Check that linked card have an id attribute. For instance, let say id="card2".
Press element button a to create a link element and assign value of
attribute href to #card2 in Attributes window.
If you want create a link to card in other deck, specify path containing the deck url and card identifier, for instance, /news/news.wml#card2. Unless specified otherwise, upon navigation to another deck, the first card is displayed.