Well for starters welcome and congrats on the new tank. Sumps aren't hard, it's basically your filter just like a canister in freshwater just the lid is open. Typically the sump will have three sections, possibly two. If it has three then you need to check out the dividers, typically there is a chamber at one end that has a single pane of glass dividing it from the next section- that's the drain section typically and is where the tank water enters. The middle section is known as a refugium and the last section is generally separated from the refugium with 3 panes the middle of which is raised (called a bubble trap). This is the return section where your pump will go to pump water back up to the tank.
If you could post a pic of the sump we could help id the sections.
Now there a couple considerations and investments that are worth every penny and ill cover those after I cover some basics.
Firstly saltwater and reef tanks differ from freshwater by having live rock and sand. These are your bio filter media and what consumes all your fishes waste (poop). It is recommended to have 1.5 times your tank volume in love rock in the tank and sump. So in your case you would want approx. 150 pounds of rock. Now you choose to buy live rock or dry rock (aka base rock). Live rock is expensive and usually comes with unknown creatures ranging from crabs and worms to coral, some good and some bad. Dry rock will become live by cycling the tank and doesn't include the extra critters, less risk and also much cheaper. Typically 8-10 dollars a pound for live, 2-3 dollars a pound for dry. When it comes to sand it's your choice, most people shoot for about 2 inches of sand which is typically about a pound per gallon of tank volume, so 100 pounds for you. You can also go big here and buy "live" sand which is also more expensive and some people doubt the sand actually having living organisms in it. You can also buy play sand from the hardware store which is the cheapest (and looks poor) or you can go middle of the road and get crushed coral or aragonite sand which is actually white.
Now that is covered we need go over water flow. Once all the rock and sand are in you need to have water flow for it to do its job filtering your water. This is done with circulation pumps, aka powerheads. As a general guideline you want to have at least 10x turnover on a fish only tank so you would want 1000 GPH of combined flow. 2x 500gph powerheads or 4x 250 GPH. Now once you factor in coral you have to increase flow, for soft coral and large polyp Stoney coral ( aka softies and LPS) you want to aim for at least 20x turnover so a combined total of 2000 GPH. For small polyp Stoney coral (SPS, colorful sticks) you want at least 30x turnover so 3000 GPH. Also once you start considering coral you have to also consider ligbting. For softies and LPS you can have moderate lighting but for sps coral and anemones you need intense lighting. Since I mentioned it, anemones don't do well in tanks until the tank is about a year old as the water parameters tend to fluctuate to much on younger tanks. Your lighting may be ok but we would need details such as how many bulbs it has, if each bulb has it's own reflector, wattage etc....
Now the basics are done let's cover some valuable investments. Firstly you will want a protein skimmer. This device removes fish poop, excess food and other bad stuff from the water. Another worthy investment is an auto top off system. This will keep your water level stable and avoid salinity swings. It will mount in the same section as your return pump in the sump. Another worthwhile thing to spend your hard earned money on is a RODI unit. We use rodi water in our tanks to avoid adding extra nutrients and contaminants to our tanks. You mix the salt with the rodi water and you have everything you need without the things you don't need. FYI rodi means reverse osmosis de-ionization. Also a recommendation on the topic, don't use tap water. Buy bottled water from the grocery store, buy the rodi unit whatever you need to just don't use tap water. It contains nitrates and other dissolved things that lead to algae growth.
Hope this helps, any other questions feel free to ask and we will help as much as we can.
