Quite easy as ive done below myself Go into edit my signature & put something like eg
click here for fanzine >> highlight it all then select from above the 'world with goggle looking thingy' icon next to B I U A, quote sign it openes an url for you to enter your URL >> then click ok when done, then it will underline it for you once its done & hover mouse over to see your URL link at bottom of screen or click it to test & should bring you to your URL so you are done
Hope that helps