The sonnet is arranged into 3 quatrain and 1 rhyming couplet, which mean the structure is the shakesperean model of writing. 

 Each stanza is characterized by an alternating rhyme, which is not potrayed in the last stanza, where there's a rhyming  couplet.

The important words of the first stanza are "yellow leaves", "a few", "boughs shaken by the cold", this words refer to autumn whuch is the season where summer ends, and the hot weather is replaced by the cold one. He interpretes birds as human beings, by adding them the adjective "naked". 

In the first stanza the speaking voice refferes to himself/herself as he/she is a season, which is getting old as time is passing by. 

In the second stanza the speaking voice refferes himself/herself not a season anymore but the lifetime of a day, which born with the raising of the sun and dies with the sunset.

He admits he is getting old so he warns us to be ready to lose someone we love