Fixing a leak can be very easy depending on the size of leak. Any leak up to 3mm is very quick and easy to do, first and foremost always follow the instructions on the waterbed repair kit. We find that most of the time a drop of waterbed repair glue does the job. Maybe if you are the belt and braces type put a small patch on that came with the repair kit but you can decide whether it needs that. The waterbed repair kit glue is designed to slowly melt the vinyl around the hole back together again. Effectively welding the hole together.
I would definitely advise you never to use things like super glues or inner tube repair kits or silicone sealants. Because these products have a tendency to dry out the vinyl and prematurely age harden underneath the glue. Large leaks can be difficult to impossible. Up to a 10mm hole you should be able to fix the leak by smearing glue over the back of the patch generously and holding it down over the hole for 30 minutes or until the glue has gone off.