A brilliant place to start is worth Learn To Play Bridge 2, by our very own Fred Gitelman. You can access it through 'Explore Bridge' -> 'Learn to Play Bridge' from the BBO lobby. Or you can download it from various places to be able to use it offline, but I can't remember where right now. It covers signalling starting from scratch, so is very useful to anyone starting out, even if you are going to switch to another method of carding afterwards (UDCA, 3/5, whatever). Dom