This Caribbean island is actually comprised of two countries, Saint Martin (French), and Sint Maarten (Dutch). Lore says that two appointed walkers from each side, starting from extreme opposites, would walk towards each other and where they met defined the land border of the two countries.
Off the ship
Your ship will dock at the cruise port in St Maarten, near Philipsburg. The ship will dock at a pier where you can walk off, and follow the sidewalk into town where you can access the beach, shops, and restaurants. It is easy enough to make a day of it without booking an excursion.
The walk from the ship is less than a mile (about 15 minute walk) or a mile if you are heading towards the middle of the beach (about 22 minute walk).
What to do in St Maarten
There will be a lot of vendors trying to sell you things all along the beach, just get use to saying no thank you. Once you find a place to settle, then I suggest having a look at the offers if that interests you. But have a look around first.
Along the beach front are candy colored builds, full of bars, restaurants, and boutiques. These include: Hard Rock cafe, beer cycling, creole food, museums, and a lot of jewelry stores (the typical cruising options).