How to Solder Copper Pipe Video
Mix up the solder flux or paste in case it has separated. Take the solder paste brush and apply the solder flux onto the pipe and inside the fitting. Assembly the parts to be soldered and heat up the torch. Acetylene or propane soldering torches work great. Apply torch to the joints for several seconds. Once the joint is hot, remove the torch and touch the solder to the joint. The heat in the pipes will be enough to make the solder flow into and around the joint.
Once finished, use a rag to clean up the joint. Be sure to remove any excessive flux. It flux is left on the pipes, it could corrode the pipe and cause a water leak.
Using the proper tools and taking your time will result in water tight seals every time.