There's several writeups on how to do it online, just google it. I use a 2 liter bottle, add 1.5 tablespoons of salt, a pinch of baking soda, 1/8 tsp of brine shrimp eggs, and add aeration to keep the eggs moving around in the water.
After about 24 hours or so, I turn the air off, wait 10 min for the unhatched eggs to sink and the egg casings to float, then I take a syringe or turkey baster and suck the live brine shrimp out of the middle/near the bottom. I squirt that into a coffee filter and if I didn't get too many egg shells/unhatched eggs then I just dip the filter into the tank that needs fed.