A camper lies in the dark in the desert, and all there is to do is listen. In just three short lines, the speaker tells us that small sounds are coming from somewhere out in the sand. We never learn what they are. They might be insects, lizards, or the wind moving grains around, and the poem doesn't try to say.
That's where the feeling comes from. The word "discreet" is a surprising choice for noises. It suggests things that are quiet and careful, almost as if they don't want to be noticed. It makes the desert seem alive, but secretive. The speaker doesn't sound frightened, though. The tone is calm and attentive, like someone holding still so as not to disturb anything.
The mood is hushed and a little mysterious. The title, "Camping," sounds ordinary, yet the poem turns it into a moment of close listening, where the night is full of life you can hear but never quite see.