The poem sets two kinds of making side by side. The robins have a nest, something built and finished, a home. The speaker has only "my plain hands," with nothing obvious to show for them. It's a small, slightly wry comparison, and it sounds more like quiet noticing than complaint.
The second stanza lifts the view upward to the alder, "high against the world," a tree standing out against the sky. Then the poem turns inward: the speaker is "passing through books / all evening." Where the birds build with twigs, the speaker's hands turn pages, and the work is reading rather than making. The title, "Hands-on," plays against that, since reading is a gentler, less physical kind of handling.
The mood is calm, modest, and a little self-deprecating. The speaker seems content to watch the natural world from a distance and spend the evening with books, though the word "plain" hints at a faint wish to have something more tangible to hold.