When transporting it home, try not to bump it around too much, as movement can be very stressful for the fish.
-Wait before releasing your fishOnce home, do not release the fish into the new water straight away. The temperature of the water in the transport bag and in the fish tank must be the same as not to shock the fish. This can be done by floating the bag with the fish in it in the fish tank for 10 - 20 mins. Then, you can slowly tip the bag and allow the fish to swim out into its new home...
voila! You now have a pet fish!