Three short lines tell a tiny story: a ship's captain comes upon sand, which is to say land, and has almost no reaction. The poem's twist is the comparison "like any fish." A fish lives in water and has no idea what a beach is. So when the captain meets this strange new thing, he doesn't conquer it or announce it or make a speech. He just wonders.
The title, "Landed," plays on two ideas: arriving on land, and the way a fish is "landed" when it's pulled out of the water. That second meaning hints that the captain is out of his element, a bit helpless and bewildered.
The mood is quiet, gently funny, and humble. The speaker seems to look at a grand moment of discovery and shrink it down to something small and human. Instead of a heroic explorer, we get a creature standing at the edge of its world, staring at something it can't yet make sense of.