Here's how to install a hot or cold water shut-off valve under your sink. Apply plumbing sealant to the shut-off threads and attach it with a nut from the faucet tube. Measure the length of the copper pipe you need to connect the shut-off valve to the coupling in the floor. Finish the job by soldering both joints.
For more on plumbing, consider:
How To: Install a New Kitchen Sink
8 Common Water Problems-and Their Cures
Top Tips for Troubleshooting Low Water Pressure