Copper pipe needs to be cleaned before it can be soldered. First, use sandpaper to clean the inside and outside of the pipes and fittings that will be joined.
Next, use flux to remove impurities from the inner and outer surfaces of both pipes. Spread the flux over the entire surface with a brush. Then, slide the two pieces together.
While wearing safety glasses, fire up the propane torch. All three parts of the flame should be blue; if the flame is orange, turn gas down.
Hold the flame on the tip of pipe to heat. The flux will turn to liquid and the pipe will change color slightly. When the pipe is heated, touch the soldering wire to the joint. If done correctly, the solder will be drawn into the joint.
Once the joint is soldered, use a wet cloth to clean up the area.