Alright,
Use either RO/DI,or distilled to mix salt water and top off.I like to mix mine to a salinity of 1.026.Dont use tap water,there to much junk in it thats bad for your tank.
Dont use any additives unless your testing for it.Once your cycles done,test for calcium,alkalinity,and magnesium and dose those as needed.With a good quality salt,you shouldnt have to much if any additives.
You'll need something to start your cycle.Either use uncured live rock or a piece of raw table shrimp.Just drop it in and let it rot.Once you do that,start testing for ammonia.When you start getting a reading for the ammonia,pull the shrimp out.Nitrite should start to climb.Its produced by a bacteria that feeds off the ammonia.Then you'll see nitrates climbing.
Once ammonia and nitrite have spiked and fallen back to 0,your cycles complete.At that point,do a 50% water change and invest in your first hardy fish.
Hope I didnt cause to much confussion.