I can give you a quick, general list: Tank, filter, some sort of cover, (cardboard will do for us poor folks) and gravel. That’s really it, I run a goldfish tank with less than that. Heaters are a good idea if your tank is in an area where the temperature changes a lot, or it stays too cold for your fish. Fish like goldfish and Zebra Danios, being coldwater, don’t need one.
It is a good idea to give your fish some places to hide. Avoid any hole that they may try to get through and get stuck in, and beware of shells that spiral down smaller and smaller. A fish can get stuck inside and die. Generally, plants are the best, fake or live. The fish don’t necessarily have to be have to hide under them: behind or between will do just as well. Caves are always nice.
I’d like to say at this point that buying gravel at an aquarium store is generally not smart. Pea gravel is available at Home Depot and other stores of that sort for about 1/5 the cost of aquarium gravel, and it’s perfectly safe if you rinse it well.
For much more information on getting started, please see Basic Aquariums – (https://www.petfish.net/kb/6/)