An emergency plumber can easily solder a pipe for you. However, if you are curious as to how this process is done, then feel free to read the corresponding steps below this paragraph.
Place some flux (lead-free)
You should be able to apply this chemical thinly to the pipe fitting’s interior and to the exterior of the end of the pipe.
Join the fitting and the pipe
Do this step and scatter the flux by slightly twisting the two materials.
Get some solder
From the solder roll, get 8 inches of the material. Bend the solder wire’s end so it would be able to reach the joint easily.
Get a propane torch
Slowly light this tool up. Take a look at its control and make sure that the torch only has a small flame. This would prevent you from accidentally starting a fire.
As you can see, soldering a copper pipe is a task that should only be done by a professional emergency plumber. You are only allowed to do it if you are skilled enough and you can assure that you would never burn your home in the process.
Move the torch around the fitting
Perform this step until the fitting is hot enough. You would know when to stop when a fresh solder is able to melt when you put it on top of the heated pipe.
Wear protective gloves in this stage of the procedure since the pipe can be as hot as your new boilers. Also, keep the torch away from your face as much as possible.
Spread the solder
Now, run the solder to the other parts of the pipe. Allow it to melt until it reaches the joint.
Wipe the joint
Get a rag and wipe the joint. Be careful since that pipe can still be hot up to now. Also, make sure that the soldering process was properly done by checking all sides of the joint.
Test the joint
If you have soldered the joint the right way, then it should have no leak when you already switch on the water supply. Otherwise, you would already need an emergency plumber to do the procedure all over again.