The reason a flaring tool exists is to cut a piece of soft copper tubing, apply a flare fitting, and provide a waterproof seal without soldering. It is often preferred to use flared copper pipe when water or gas will be going through the tube.
Choose the pipe you will use to make the flare and put the nut on the tube before breaking out the flaring tool.
Select the size you need to use (for the pipe) on the clamp end of the flaring tool. A standard-sized flaring tool will clamp six different sizes of copper tubing (between 3/16 and 5/8 inches).
Hold the flaring tool while you put the pipe into it. Keep the pipe end flat against the tool. The coned part of the flaring tool needs to go onto the tubing. Put the clamp end on the end of the copper pipe.
Turn the handle on the flaring tool until you have gone through the pipe.
Remove the tool and check the cut edge. If it is smooth, you are good to go; if not, do it over.
Produce a seal by clamping and tightening the tubing with the flaring tool. The copper tubing will flare out and produce a seal by filling any rough areas that are on the nose.
Apply a flare fitting using the flaring tool as follows: clamp the flared end of the tube next to the fitting. From here, screw the flare nut onto the fitting until finger tight.
Be sure the cut on the copper pipe is smooth. This tool works on aluminum tubing as well as copper.
Be careful while cutting, it is easy to ruin the flare and have to start over.