All round the coast the languid air did swoon, Breathing like one that hath a weary dream. (5-6)
This comparison between the "languid" (lazy) air and a sleeping person helps to set the drowsy tone for the whole poem. It's not just the sailors who don't want to move, it's almost as if the whole of the natural world is asleep and dreaming. The way the word "weary" gets dropped in there also helps to emphasize that this "dream" might not be all that pleasant, either.
Branches they bore of that enchanted stem, Laden with flower and fruit, whereof they gave (29-30)
The whole plot of this poem is driven by a plant. In order to fall under the spell of this sleepy new place, the sailors have to eat the "enchanted" Lotos. Once they do, they're totally stuck. This idea, that something in the natural world could hurt you or trap you if you eat it, doesn't just show up here. Eve with her apple and Persephone with her pomegranate could definitely tell these guys something about forbidden fruit.
And taste, to him the gushing of the wave Far far away did seem to mourn and rave (31-32)
This is another moment where something in nature takes on the characteristics of a human (we call that personification). In this case, once the sailors have chomped on some Lotos, the noise of the waves starts to sound like screaming and crying. Nature can be a beautiful thing in this poem, but at times like this it also starts to seem scary and sinister, too.
There is sweet music here that softer falls Than petals from blown roses on the grass, (46-47)
Okay, we just brought this one up because we think it's a really pretty image. The speakers of these are comparing the sound of the music in this enchanted land to the softness of a rose petal falling on the grass. We can't imagine much of anything more gentle and lovely and calm than a single petal dropping on the ground. It kind of makes us want to hear that music, and maybe try some of that Lotos… No! Bad! Must… not… eat Lotos…
To dream and dream, like yonder amber light, Which will not leave the myrrh-bush on the height; (102-103)
As the sailors sing their song, they pick up images from the beautiful landscape around them. Here they use the light of the enchanted, endless sunset as an image of the endless dream they want to fall into. Nothing works quite the way it's supposed to in the land of the Lotos-eaters, and even time and light get twisted and stretched in strange and magical ways. Like everything else in this poem, the natural world seems kind of lovely and kind of scary, too.