Do you mean like this http://pokemondb.net/pokebase/meta/15141/how-do-i-add-a-web-link-to-my-answers?
Or do you mean like this?
Well either way all you need is the Url of the website which is found at the top (Web address) click it and that will highlight it then simply copy it by using Ctrl C.
Ctrl V to paste the link into your answer/question.
But otherwise you can press Ctrl L (or the icon with the globe next to the Italic button)
And then a box will come up simply paste the Url into that box.
Then you should have something similar to this enter link description here.
Simply delete the text and customize it like this Cat rolling in Money