This is not exactly an easy task. It takes time and a lot of organization. Start by making a list of all the electrical outlets and electrical appliances in the house. Try to be specific when it comes to the outlet locations. Usually most of the outlets in a room will be controlled by one switch but sometimes they are different.
Once you have your list, start going through the switches one at a time. Turn off the first switch and go around to see what turned off. Once you find the room or location, test all the outlets in that area. You can use something like a night light or a cell phone charger to test if the outlets have power or not. Record the number switch next to everything that is controlled by that switch. Then proceed to follow the same test for each of the remaining switches.
Once you are done, you should have a complete directory of all the circuit breaker switches and what they control. This is very important information to have handy in case you need to replace any electrical appliances or do any electrical work. It is best to know what all the switches do before you actually need to use them.
You can write the functions on the label that is in the circuit breaker or do what I did and type up a new one that is clear and organized. Once it is typed and printed, cut it out and tape it inside the panel cover so you or anyone else who needs it will have the correct information for the circuits.