Hi my name is Jordan.D and if you are new to fish I will guide you to making a wonderful aquarium.
Step1: Research about what fish you want. For example you might wan't a semi agressive tank then you search "Semi-Agresive Tank mates" and find out what fish could live together. Remember there are 3 types of behaviour in fish: community, Semi-Agressive and Agressive. Don't keep Semi-Agressive or Agressive with community fish it will stress them out.
Step2: After researching buy decorations that match your desired fishes habbitat. For example Cichlids like stones and sand not plants and gravel.
Step3: Buy these supplies: Sand/Gravel, Water Conditioner, A siphon hose, Filter, Filter pad(usualy comes with filter), buckets and fish food.
Step4: Ask a fish sales men about the type of food to get your fish. There is an easy way of telling what kind of food your fish need If they swim at the bottom you should get sinking pellets for fish that swim on the top and in the middle, flakes and floating pellets are the best.
Step5: Add the gravel/sand in the tank.
Step6: then add the decorations in the tank.
Step7:fill the tank with water using your siphon hose.
Step8: Attatch Filter (with the pads inside) to the side of the tank.
Step9: get a cup of water and poor it into the filter until it starts sucking water up and letting it out.
Step10: Messure how much water conditioner to put in your tank. Once you have done it poor the right amount of water conditioner in the tank and wait about 2 hours until its clean.
Step11: after 24 hours you can purchase the desired fish(best if you buy 3 every week).
Step12: After two weeks of having your aquarium you should purchase an Algae eater, they will eat algae. These are the best algae eaters for these tanks:
Plecostomus Max Size 28" great for semi agresive tanks.
Golden apple snail Max Size 3" great for community tanks.
Otocinclus Max size 2" Great for community tanks.
CAE(Chinese Algae eater) Max size 5" Great for aggresive tanks.
Congratz You have an aquarium! :D