The flourescent light that comes with the aquarium will be enough for fish only, but you'll have to upgrade in the future if you decide to add corals. Very few corals will survive under the single T12 or T8 tubes that come with most barebones aquariums. You MIGHT be able to get mushrooms to live longterm under that light, but even that would be tough. A sump is basically a tank under your tank to help increase filtration and water volume. melevsreef.com can teach you more about sumps than I can 
