You need to get an API Saltwater Master Test kit and start testing your water. You also need to give the aquarium and ammonia source for it to start cycling. Once you give it the ammonia source then it will start to grow Beneficial Bacteria (BB on here) that will break that ammonia down into Nitrites. After a while your Nitrites will build up and more bacteria will break the Nitrites into Nitrates. After a few weeks, you should be able to test your water and the ammonia and Nitrites will test at 0 ppm
. The Nitrates will test higher so you'll have to do a big water change THEN you can add life to the aquarium. if this didn't make sense then just google cycling an aquarium and studying A LOT about it. It is also called the Nitrogen Cycle.