At the top of your internet browser there should be a long white bar. Inside there is usually an address looks like "http://www.monsterfishkeepers.com" Copy the whole thing. Easiest way is to highlight the entire URL either click at the beginning with your left button on your mouse and drag to the end of the URL or double click inside the bar with the left button or click into the bar and press CTRL + A and then to copy is ctrl + c or Edit > copy. Then go to the Edit screen and edit your signature. Type in [ URL] paste in the URL that you copied, then end it with [ /URL] *minus the spaces.
see my sig. type up the word you want "linked". highlight the word you want linked, then click on the hyperlink symbol. paste the link in the window that pops up.