Go over your ideas of what you want with a knowledgeable employee. Seek opinion about what you want. Even armed with lots of information you may pick products that are overpowered or overpriced or just unnecessary. For freshwater the basics are a tank, a lid, a light, a filter, a heater, possible an air pump and stone, gravel/sand, water conditioners or prefilters, and fish. Saltwater involves a tank, lid, lighting, many water conditioners and additives, a protein skimmer, sand/gravel, salt mix, and many other items.