Please STOP AND READ THIS. I know you are in a hurry to find out how to solder, but today is not a good day to die, or burn your house down.
When using an open flame, it is so easy to start a fire, or get a severe burn. Make sure you have a fire extinguisher at arms reach before you light the torch. Make sure you have on eye protection, one drop of hot solder in the eye is all it takes to loose the eye. If you have long hair, make sure you tie it back, If you have loose clothing make sure to tie it off or remove the loose items. Make sure there is no gas leak on the torch, make sure there are no flammable liquids or gas tanks in the working area, this includes paint cans, paint thinner, gas cans and any other. Make sure the area is well ventilated. If you will be working in a tight area very close to wood and especially if you will be working on a pipe that comes through a hole, from the floor above, you can start a fire in the sealed walls above and not know it till it is far too late, In a case like this the fire extinguisher may be useless, because you will not be able to spray the base of the fire with out breaking the wall open.
There are many other possible ways of causing damage and getting injured You will be far better off calling a professional.
Please don't take my warnings lightly. Read and follow the instructions below at your own risk, I am not responsible for any thing that may happen as a result of your trying to solder. You assume full responsibility for anything that happens.
The first thing that is very important is that all the water is out of the copper lines. the water may take a long time to stop dripping, you may need to open a faucet or valve lower then the pipe you are working on, and you may need to use a compressor to blow the water out of the lines.
It's better to use a pipe cutter to cut the pipe, if you use a saw blade make sure you remove all the burs, If you use a pipe cutter you will still have to remove the bur inside the copper pipe. Once the pipe is cut you will need to clean the end of the pipe with emery cloth, clean at least 1/4" more then the new fitting will cover, (for 1/2" pipe clean at least 3/4") You will also have to clean the inside of the fitting, Both pipe and fitting must be cleaned all the way till the copper is shinning, any old solder or dark spots have to be removed.
Make sure not to touch the cleaned area with your fingers, the fingerprints may prevent the solder from taking to that part of the pipe. Then use a non corrosive soldering flux I like Oatey number 5. Using a small acid brush put a thin coat of soldering flux over the area that will be soldered. Make sure to cover the whole area on the pipe and inside the fitting.
With all the fittings cleaned and fluxed and dry, its time to light the torch, But before you do that make sure you are using the right type of solder for what you are working on, If you are working on any potable water line (drinking water shower water, any water that may be used for drinking bathing or cooking) You Must Use A Lead Free Solder, 50/50 solder is 50% lead and must not be used on any line that connects to or is a part of a potable water supply.
Make sure the solder says lead free, lead free solder needs more heat to flow but it makes a better longer lasting sealed joint. Now light the torch, move the flame all around the fitting (as is possible) This is the big trick, Don't melt the solder with the flame of the torch!!!!! The pipe and the fitting need to be hot enough to melt the solder on contact with out the flame on the fitting at the time, you will need to test as you go remove the flame touch the solder to the joint, if it does not flow, remove solder and reapply heat, and go back and forth till the solder flows, be careful you can over heat the fitting, if you do over heat the fitting, you will have to let it cool, take it all apart re clean and reflux, just adding more flux will not work and will cause a leak
Once the solder flows around both sides and you have a little bead at the bottom to the joint, you are done, don't keep trying to be sure, you will just be wasting solder and increasing the chance of over heating the fitting.
Once the solder becomes solid again, (it will go from shinny to dull) use a very wet rag to remove the excess flux from the fitting, it's best if this is done when the pipe is still very hot. If you don't remove the excess flux, the next day all your new work will be green.
I hope this page and this website has been helpful to you.