I have a 30-year-old home, and some of the shut-off valves are stuck...so I couldn't turn off the water if I had to. I'm afraid to use a wrench or something to force it, for fear of breaking it. Is there an easy way to fix these valves?
These are probably chrome-plated brass shutoff valves that have frozen open due to corrosion or mineral buildup over time.
You should be able to loosen the handle with a pair of channel-lock pliers. Just grip the whole handle in the channel-lock teeth and turn it clockwise steadily until it loosens. It shouldn't break.
These are probably due for replacement. If they're on copper lines, you can use compression fitting valves without doing any soldering.