The poem starts with an epigraph (sometimes written out as a subtitle) that sums up its main idea. This is a "Description of Spring," a season "wherein" (or in which) "each thing renews, save only the lover." In other words, spring is a time when everything is refreshed and rejuvenated—everything, that is, except for "the lover." Right up top, the poem implies that the speaker's lover has decided to end their relationship (to not "renew" its terms).
The poem itself then begins by declaring that it's the "soote," meaning "sweet," season, that time of year "that bud and bloom forth brings." Gone is the barren misery of winter, replaced by the sweet delights of spring. The bright /b/ alliteration of this line evokes the way that fresh growth and color burst forth in spring:
The soote season, that bud and bloom forth brings,
Spring has "clad," or clothed, the hills and vales with "green," the speaker continues. The speaker is subtly personifying both spring and the landscape here, granting it agency and purpose: the season gently cloaks every inch of the land, from tall hills to deep valleys, in life.
It's not just the landscape that renews in spring, either: animals, too, are rejuvenated by the shifting season. The "nightingale," decked out with fresh feathers, "sings" her song, while the turtledove warbles out a tune to her "make," or mate. Again, the poem's sounds help make its imagery more vibrant. Listen to the alliteration and consonance of line 4:
The turtle to her make hath told her tale:
Those flitting /t/ and lilting /t/ sounds recreate the bright, joyful music of spring's natural orchestra. The mention of the turtledove's mate, meanwhile, is a sad, subtle reminder that the speaker's own beloved has left.
"Description of Spring" is a sonnet. (Henry Howard played a major role in the development of the sonnet in English-language poetry.) This opening quatrain features an alternating, ABAB rhyme scheme and is written in iambic pentameter: a meter containing five iambs, poetic feet with a da-DUM rhythm, per line.
The soote | season, | that bud | and bloom | forth brings,
With green | hath clad | the hill | and eke | the vale:
There's a trochee (the opposite foot of an iamb, DUM-da) in the second foot of line 1 ("season"). This adds some emphasis to the word "seasons," subtly conveying spring's power. Overall, though, the regular rhyme scheme and meter lend the poem a steady, propulsive music.