William Shakespeare's "Sonnet 2" is written using iambic pentameter (five pairs of iambs, equally ten syllables). It contains fourteen lines (three quatrains and a couplet). The first twelve lines contain an alternating rhyme scheme. In every four lines, the first and third / second and fourth rhyme. At times the rhyme may not be an exact rhyme, then sight rhyme takes its place. The last two lines, the couplet, rhymes with itself.
The first eight lines provide a problem or story, line nine (the volta or turn) signals a change in the subject matter of the poem (sometimes offering a solution). Sometimes though, Shakespeare would not place the volta until lines thirteen and fourteen, using the poem;s entirety to lay out his thoughts. This delay is what happens in "Sonnet 2."
As for the poem itself, the speaker is examining the idea of aging. The speaker is worried that time will age his or her face before he or she realizes it. Therefore, a son must be born to carry on the beauty of the family (without the furrowed brow--wrinkles).
The poem uses alliteration ("dig deep"--"d" sound repeated), assonance ("proud" "now"--"o" sound repeated), personification ("winters shall besiege"--winters cannot attack something in the way people can), and metaphor "dig deep trenches" refers to wrinkles).