Threaded shut off valves are pretty easy to install they simply thread onto the pipe.
To help you get the right shutoff valve for the pipe you are installing the threaded valve onto, here are a couple ways to determine the pipe size.
Pipes are labeled for there size with either I.D. or O.D.. I.D. (Inside Diameter) would be the inside diameter of the pipe. O.D. (Outside Diameter) would be the outside diameter of the pipe.
Most threaded shutoff valve's use the O.D. measurement.
Tool's required for installing a threaded shutoff valve would be a pipe wrench, adjustable crescent wrench, thread tape, and some plumbers pipe dope
Installing Threaded Shutoff Valve
Step 1.
Wrap thread tape around the threads, then apply a light coat of pipe dope on top of the thread tape.
Step 2.
Thread the valve onto the pipe hand tight. Then using the pipe wrench to hold the pipe from turning(if possible), and use the crescent wrench to tighten the water valve.
Step 3.
Install the water supply line for the fixture to the water valve.
Step 4.
Turn the water back on and check for leaks.