Jeff welcome to the site.
Glad to hear that your doing your research before you get your tank.
Depending on where you live and your general water quality you can use tap water but I find best results if you use RO
water and then add your salt mix to this. The reason is that the salt mix adds trace elements to your water and if you already have trace elements in your water supply you could have issues with to many elements and thus an algae problem.
To make your first batch of water you can just add the freshwater to the tank and then add the salt mix slowly to the freshwater. Only do this the first time. When you add saltwater when doing water changes make sure you mix the water up atleast 24 hours in advance.
Have your powerheads and heater running when mixing the salt as warm water mix's better than cold water.