first you will need to add sand and live rock so you can begin your cycle
Cycle your salt tank - Aquarium Advice
while your cycling you need to decide what type of fish you like
as there are both not reef safe fish and reef safe fish.
if deciding on a reef be sure you get a light capable of supporting coral
most important part is to take it slow not to overload the new tank with fish all at once.
I wouldn't recommend a canister with a reef as they are considered nitrate traps.