When it comes to your plumbing, there are different types of issues. Some might be minor, but there are some that can truly be designated emergencies. This is what you would call a situation where you have sewage backing up into your home, or gallons of water gushing from a broken pipe.
There are usually very few things you as a homeowner can do about fixing these kinds of disasters, but you can do what you can to minimize the potential damage.
You will find that the best thing to do right away is to turn off the water supply. Knowing where this is located so you can do so quickly is important, but you might not always need to go to the main shutoff valve. Often you will find shutoff valves in critical locations, and as long as the valve is on the right side of the leak, turning off the valve will help.
Shutting off the water will even help in a situation where sewage is backing up. You will find that it is very easy to accidentally run water or flush a toilet without thinking about it, making the situation worse, so keeping the water off until the problem is resolved is going to be the best thing to do.