Help me to analyze meter, rhyme scheme and understand the meaning of the poem "A Late Walk" by Robert Frost.

Let's start with the mechanics.  The poem is written in
quatrains, or four-line stanzas, in which three-beat and four-beat
lines alternate.  This is a traditional form; see the Wikipedia reference
below.

The rhyme scheme is a, b, c, b:
only the second and fourth lines of each stanza rhyme.

The
mood is rather somber, reflecting the season, which is autumn: whence the "late walk". 
In stanza I you have

The
headless aftermath

of the
harvest, suggesting death that happened a while ago.  In stanza II there
are

sober
birds

and

withered
weeds

In stanza III you have
the tree with only one leaf left hanging, which falls as the poet
passes.

Stanza IV changes the mood considerably: the poet
picks "the last remaining aster flower":  although faded, it is his gift of love to
somebody who appears in the last word of the last
line.

Here are some other interesting devices the poet
uses:

In stanza I, "Smooth-laid like thatch with the heavy
dew" is rather heavy itself with many accented feet.  It suggests the poet is wading
through this deep thatch of straw.

Stanza II uses
alliteration: "garden ground", and "withered weeds".  Alliteration was used in some of
the old epics as a kind of rhyme, where the beginnings of the words, rather than their
endings, would match.  Again, "Up from the tangle of whithered weeds" has an abundance
of strong feet which tend to tangle your tongue.

Stanza III
user personification: the tree "stands", a leaf "lingers", is "disturbed", and "comes
down".  Here this device draws immediate attention to the tree and the leaf, while the
wall fades into background.  Again we have alliteration: "beside", "bare", and "brown";
also "disturbed" and "doubt".  Also internal rhyme -- which may be accidental -- of
"not" with "thought".  Come to think of it, some internal alliteration: "s" in
"beside","stands", "disturbed", "comes" and
"softly".

Stanza IV uses alliteration again: "far", "from",
"forth", "faded", and "flower" (which contrasts with, and sets aglow, the sound of
"aster").

In each stanza the third line seems to stand out,
which helps to point out the significance of "the last remaining aster
flower".

So: with all this analysis, we've chopped the poem
into tiny bits.  But now read the poem again, as a whole: savor its goodness, and maybe
let all this analysis add just a hint of additional sparkle.