An angle stop is basically a shut off valve for a sink fixture. As the hot and cold water supply lines come out of the wall, they are capped while the wall covering is installed. Once that is finished, you can remove the caps and finish the plumbing installation or your sink. To do that you must install the angle stop valve.
Step 1: Cut off Copper Cap
Use the pipe cutters and cut off the cap on the end of the copper pipe. Once the cap is removed, sand off any of the burs and jagged edges.
Step 2: Insert Compression Fitting
In order to get the angle stop to sit correctly, without any leaks, on the copper pipe, you should use a brass compression fitting. Insert it onto the pipe and slide it enough so you can place the angle stop on the end.
Step 3: Attach Angle Stop Valve
Slide the angle stop onto the copper pipe. Make sure that you push it onto the pipe as far as it will go or it will not set correctly. Connect the compression ring onto the angle stop and tighten the nut. You may need to use two pliers in order to snug up the nuts on the fitting.