Now fades the glimm'ring landscape on the sight, And all the air a solemn stillness holds, Save where the beetle wheels his droning flight, And drowsy tinklings lull the distant folds;
So what's happening, exactly? The "glimm'ring landscape" is fading from the poet's sight. Must be sunset, but we knew that from the first stanza.
The air is quiet, too, except for the buzz of the occasional beetle and the tinkling bells hanging around the necks of livestock in their "folds" (a.k.a. barns).
Sounds peaceful and sleepy, like everything is winding down.
There are some interesting literary devices in these lines, too: "solemn stillness" is a great example of alliteration, and the speaker personifies the "tinkling" of the bells when he says that they're "drowsy." Go to the "Symbols" section for more on these literary tools!