First, go to a store you know has fish, like a pet store. Like, Petsmart. Second, estimate how many fish you can fit in your tank. A ten gallon tank, 5-7. A fifteen gallon tank, 7-10. A twenty gallon tank, 10-13. Third, always look to see if they are mean or nice. NEVER put mean and nice together... THEY DON'T MIX!!! Fourth, after you know which ones you want, wait for an employee to help you get the fish you picked out.
Fifth, tell the employee what kinds you would like. He/She will get them out for you. Sixth, Pay for your fish, and run home to plop them in their new home. They need to get out of their bags. Finally, you have a beautiful tank with live fish. And it's in your very own house.