Leaks in your plumbing system can quickly become a major issue. This is especially due to the fact that most homes have about 14 gallons of water flowing through their pipes every minute. A complete break would instead dump that inside of your home, and even though these breaks are rare, it could happen with a cut in the wrong place or a simple mistake like that.
With a large amount of water gushing out like that, it’s going to be near impossible for you to stop the water from flowing, which is why you instead should go straight for the main shut-off valve. Before you do anything that would put you at risk of damaging your pipes, you should be well aware of where this valve is located, and in some circumstances, it might be worth it to shut it off preemptively.
Knowing whether or not there are pipes in the wall behind which you are working is a good start as well. If you are working near a sink or toilet, you should check to see which direction the pipes run.