Brine shrimp live hatched?

so ive decided tht i want to hatch brine shrimp so i can feed it to my guppies/guppy fry/betta and was wondering do i just leave the eggs in a cup of water?? what do i do where can i get it?if my fish store dont have it can they order it in? is this good for betta fry as well i will be breeding my betta soon