right all of this depends on what size tank and what sort of tank you would like and the dimensions. take a look at the pinned topics at the top of this forum. Clownfish dont need an anemone and live happily without one, but sometimes the will host other things like filters or caves.
you could go for a simple marine tank which isnt all that different from a freshwater tank, just with the addition of salt and different decor. maybe a skimmer. Which are known as 'fish only' tanks as they only contain fish life.
Then you have the more advanced FOWLR and reef tanks. This is where it marine gets a bit more compilcated. With a reef more aspects of a marine tank have to be monitored and you have to get more equipment some it gets more expensive. You will need a good set of lights (not cheap, well unless you get second hand which is great to do save you money), you will need live rock (thats not cheap either) etc
If i were you i would go for a fish only, as thats what i did when i first did a marine tank. This will give you a chance to get a feel for the marine hobby and get you used to the saltwater timetable (waterchanges, FW top ups etc).
Its really down to what you are looking for from the tank