Instructions
Find a breeder net that fits your needs. You'll find them in the fish care section of any pet store and they come in a variety of sizes. They are inexpensive and rather delicate, so pick up a second one as a back up.
Set up the frame of the net according to the package instructions and then pull the net over it.
Rinse the net in tap water before you put it in the tank to remove any debris.
Hook onto the edge of the tank in an area that gets plenty of aeration but is far enough from the filter so the fish inside don't get pummeled with rushing tank water.
Consider buying an airstone and pump and placing the airstone directly inside the breeders net. This will help keep the net clean and make sure the fish inside get plenty of oxygen.
Place your fish in the net using a net small enough to get inside the breeder net so you don't get stuck and thus, traumatize your fish.
Clean the net once a month by swapping in the spare net and then rinsing the old net with tap water and using an algae scrubber to get the rest.
How to Use a Breeder Net
A breeder net is a finely netted plastic-framed cage that sits on the edge of your fish tank. If you need to isolate an aggressive fish, protect a smaller fish, or need a safe place for baby fish to grow, or to partition betas in a community tank, a breeder net can be an inexpensive alternative to a separate tank.