You type -
[U RL="http://www.bdsmlibrary.com and the rest of the address you wish for the link to go to]my stories or whatever[/URL]
but so the the first U RL does not have a gap between the letters - i.e. is [URL=
Hope this helps - if it does not make sense, send me a PM I can make the change in your signature for you; and then you will be able to copy the pattern in future.
General point - please note that whilst it is always fine to link to any page within this site, it is not acceptable to link to commercial sites or 'competitors'. If anyone is in doubt about whether it is acceptable to link to a particular site please ask one of the supermods or admins.
cariad