First of all welcome to the board,
A 50 gal is a good size to start with IMO, I think ts best to learn how to setup if you get a good book because to explain everything would take a while, there is a lot of things you need to know when starting saltwater. Its a lot easier to answer a "smaller" question but to ask how to setup would take a while to type. So I would research a lot on here, books, internet and ask questions here.
I'll just give you a few things to start with. IMO you should have live rock and live sand. Live rock is rock that comes from the ocean, it is a great source for biological filteration, on other words its like a filter for your tank, but you can't only have rock for filter, the rock just helps reduce nitrates and stuff. Also with live rock you get stuff growing on it like mushrooms, plants differnt algea, it may cost a bit but it is worth it. Live sand is also worth it, the sand if its deep enough will reduce nitrates and ammonia and looks good IMO. There is also crushed coral but that IMO is not nearly as good as sand, many people have been swicthin over to sand. Also with crushed coral you have to clean it manually and it collects eneaten food and detris while sand does not and your clean up crew cleans it for you.
You will need a test kit to check the water parameters while your tank cycles and of course you need salt, and a hydrometer (salt tester). There is a lot more about setting up but like I said its better to get a book and read all about it, or you can ask questions here.
