Patience is not only a virtue in this hobby (or, yes, I know, a vocation for many ) but a necessity. You'll find lots of great info here, and more ideas on how to spend money than you ever imagined.
A good test kit is a must have. My personal preference is the TetraTest Marine AnalySet, with the Seachem MultiTest Marine (Basic) a little cheaper but not quite as easy to use. The Salifert kits are also very good, and no one, including me, seems to like the RedSea ones.
Using quality salt mix (e.g., InstantOcean), RODI water (a search here for "RODI" will tell you all you ever want to know), and maybe a starter pack of additives, esp. if you plan on a reef or keep any iverts is good to have as well since a new systen will be shy on iodine, etc.
I've learned a lot here, and I had YEARS of experience with freshwater before- asking several specific questions usually gets you better answers than one long or broad one.