You can buy devices from the gadget section of your kitchen supply store, so you can just break the egg into the top and the whites will drain into the container below. Just be careful not to break a yolk, because that will keep the whites from beating properly.
You can also do what most cooks do, and that is to crack an egg around its equator, hold the egg over the bowl where the whites are going, and gently lift the top part of the shell off of the egg. Most of the white will run over the edge, while you cradle the yolk in the bottom half. Now gently pour the yolk into the other half of the shell, and more white will run out. Do this two or three times and then dump the yolk into a separate bowl.
Some people break the egg into their fingers and let their fingers strain the white away from the yolk. That’s OK, too. Your choice. Eggs are pretty cheap, so if you lose a few while learning, don’t worry too much.