Relieve any pressure in the existing propane lines, and disconnect them from the propane tank.
Cut the old or new line where you want to install a fitting ("T" or valve). Slide an threaded fitting over the end of the line and flare the line with the flaring tool. Repeat as necessary for the other lines that join the fitting.
Thread the fittings together and tighten them down with the crescent wrenches. Attach the lines to all necessary appliances and tighten them down.
Bury the copper pipe lines at least 12 inches underground if you use them for an outside application. Bury the lines at least 18 inches underground if there is or may be vehicle traffic above them.
Attach the modified or new propane line to the tank, and turn on the gas. If you smell any leaks, turn off the gas at the tank, wait until you cannot smell gas any more, and repair the leak by installing a new fitting or tightening the existing fittings.