Yeah, you're going to have to put in some elbow grease. If the filter is running and there's nothing living in the tank besides the Algae, I would get a product called Algaefix. It will wipe out all the algae from the tank. Turn the lights off over the tank to help kill the algae as well.
If you know literally nothing about a saltwater setup, or fish in general, you could always sell it or turn it into a freshwater (easier to maintain) tank.
If there's enough water to run the tank, I would make sure there aren't any areas leaking.
But all the equipment will have to be scrubbed (NO SOAP!) down and cleaned, the water drained and refilled (depending on if it's been sitting stagnant or running recently), all the algae done away with, the rocks scrubbed off of that crap and definitely you need a power head or two for water circulation.
That also looks like a siphon drain to the filter, which you're going to have to read up on because there are hazards that come along with that method of getting the water down below. Also, you need to know how many gallons the tank is. If memory serves correctly, it could be either a 42, 72, 90, or 110 gallon bow tank.
You can have a nice tank out of that, but I would start by taking everything apart, cleaning it so you learn how and what each piece does. A good cleaning tool for aquariums is mixing white distilled vinegar (the regular type you cook with, not the cleaning version with chemicals) with water. Usually scrubbing or soaking in a 1 part vinegar to 3 parts water is sufficient.
I apologize if I'm telling you things you know, but I don't know what you do and don't know.