Oh... they were probably talking about adding buffers and/or calcium to get the water parameters where you want them. While that may be something you'll get into later down the road, you don't need to worry about it at this stage. Many folks (including me) "tweak" their salt water instead of using it exactly as it mixes up. For me, I want to run a little higher calcium than what my mix gives me.
Adding a little more to my last post, once you mix your salt mix into your plain water, you want to "age" that for a day or so. This will insure everything is dissolved AND allow the pH of the water to stabilize. The pH of freshly made salt water is higher than normal and after a day it will stabilize to where it should be. Most folks store a certain amount of premixed salt water in a plastic food-grade tub of some sort, with a heater and powerhead in it to provide aereation and to bring it up to your tank's temperature. Real handy in case you need to do an emergency water change, or set up a quarantine tank on a moment's notice.
