Whitman makes a list of other things with which he loves to be in contact. Many of these things are also pretty sexy-sounding, like "loveroot" and "crotch."
Imagine a happy dog running around the hills and fields and sniffing everything and barking with delight, that's what Whitman is doing.
He views himself as a part of nature.
He discusses the morning and sunrise. The beginning of the poem has a sunny, airy freshness that suggests the morning.
He is singing a "song," which refers both to the poem itself (in the old days, poems used to be called "songs") and to music in the conventional sense.
He asks about our sense of size and proportion. He wants to know what we would consider to be "a lot."
He asks us about our reading habits, and we get the impression that he is being sly. He doesn't think we should be taking so much pride in book learning and in finding the "meaning" of poetry.
He's going to teach us a lesson that could be right out of Ralph Waldo Emerson's essay "Self-Reliance": you can't learn everything you need to know from books. You need to discover things for yourself.
This message is kind of unexpected because we're reading a book right now. (Well, not right now. At the moment, you're reading Shmoop, but in Whitman's day you would have been reading the poem in his book Leaves of Grass.) Maybe Whitman is trying to warn us that we need to apply his lesson about self-reliance even to the reading of this poem.