OK, If you dont already have a great book for marine aquaria, I would purchase one or head for the nearest library.
You either need test kits or a good LFS that will test your water for you.
Once you have no more ammonia, no more nitrites and measurable nitrates, you have completed a cycle. Then you do a water change, then you test everything again and then you can put in a fish.
What did you use to start your cycle? live sand or rock?