Certain word choices help to convey the concept of belonging in this poem.  First, the speaker begins three lines in the first stanza as well as one line in the last stanza with the phrase, "I am from."  Second, she begins four lines from the next two stanzas with the similar phrase, "I'm from."  This repetition of initial phrases is a type of refrain called anaphora.  A good poet will not repeat words or phrases that are not terribly important, and the simple repetition of the way the narrator identifies her origins helps to establish her sense of belonging.

Next, all of the ways in which this speaker identifies her childhood also helps to establish her feeling of belonging.  She references household chores, like laundry, in terms of what products her family uses; she identifies the items that were in her yard.  She mentions what might be a family recipe for "fudge" and what she was like in school.  She discusses church, and making a "cottonball lamb" as a child in Sunday school.  She describes her family tree, what people ate and drank, and even injuries sustained by relatives.  Finally, the speaker mentions the box of pictures under her bed, saying,

I am from those moments—
snapped before I budded—
leaf-fall from the family tree.

We understand that the speaker has described her most visceral recollections of her childhood, figurative snapshots of memory that signal her sense of what is familiar, comforting and hers.  These are the things that give her a sense of belonging, that make her feel "from" somewhere.

George Ella Lyon's poem is a catalog of images from her youth that evokes both her sense of place and strong ties to family.

The first stanza, for example, give us details about the setting of her life:

I am from the dirt under the back porch./(Black, glistening, it tasted like beets.)/I am from the forsythia bush/the Dutch elm/Whose long-gone limbs I remember as if they were my own.

In a sense, the poem has an  elegiac tone, that is, a slightly somber reminiscence of things in her life that are "long-gone," but there is also the joy of recalling place and family that demonstrate her sense of belonging  to a specific place and family.

In the second stanza, she has moved from describing her home to another aspect of her youth:

I'm from the know-it-alls/and the pass-it-ons, from Perk up! and Pipe down!

Because this stanza includes "eyeglasses," we can conclude that she refers here to school because the images she incorporates are typical of the school experience.  In addition, her mention of "I'm from He restoreth my soul" tells that she, and most likely her family, attended church because she quotes from the 23rd Psalm.

Images of Lyon's family appear in the third stanza, giving us a strong sense of the poet's memories of, and bonds with, her family:

I'm from Artemus and Billie's Branch/ . . .From the finger my grandfather lost to the augur,/the eye my father shut to keep his sight.

She has identified her family tree but, more important, she recalls concrete details about her grandfather and father, details that evoke specific images in the reader's and transcend the abstract.  She doesn't say, for example, that her grandfather and father suffered physical problems, she tells us exactly how they suffered, bringing them to life for us and she does for herself.

The main theme of the fourth stanza--family pictures, some she cannot identify--resonates with most of us.  The box underneath her bed a "a sift of lost faces" because they were taken "before I budded--/leaf-fall from the family tree."  She recounts here a typical experience from childhood--a collection of family pictures, some of which are of strangers (even though they are family) because they are "long-gone," to use a phrase from the first stanza.

The poem, which has stimulated a lot of interest and is used as a model for students to write autobiographical poems, is a beautiful evocation of a strong sense of place and family, of belonging.