The Marina Piccola is where the ferries and hydrofoils dock. To get there you can walk down several hundred steps (well, that's what it feels like..I didn't count), walk down a switchback hairpin-bending road or take a bus from Piazza Tasso (the main square).
There are a couple of cafes/bars, and a tiny bit of sand, and a great deal of evidence of how the cliff face has been used in the past for storage, building and so on. It's quite amazing to see existing buildings literally clinging to the sheer rock faces.
To the left is the Marina San Francesco, with a myriad of small landing stages to wander past, to the right the large concret quay which functions as the ferry/hyrdofoil stop.
You'd probably only go there to catch one of the ferries/hydrofoils, but it is worth allowing yourself some extra time to have a bit of a wander along the quaysides. Do some people-watching, gaze into the super-clear water to see the fishes, look at the cats enjoying their seaside existence (fishy titbits from the fishermen, I suspect!). Maybe have a glass of something whilst sitting in the sun gazing over the bay to Vesuvius and Naples.
A pleasant place to sit awhile and watch the world go by.
Marina Piccola or small marina is where you go to catch the ferry or hydrofoil to nearby towns & islands e.g Naples, Capri. You can find many sales booths or counter selling tickets on the ferries or hydrofoils
The area itself is pretty, with a small park with trees & flowers. There are also some restaruants that serve coffee and mail meals if you are hungry.
Be warned, I walked from the top to get to the marina and the walk up on the long steps was exhausting!! Remember to wear good walking shoes!!