Decode Shakespears Sonnet for me?

One of Shakespeare's more popula sonnets, personally one of my least favorite. Sonnet 18 is quite simply saying that the person of focus or more then likely the women is more lovely then a summer day. Summer day's have many flaws in shakepeare's opinion and they come and go with the seasons. But the beauty that this women possesses is eternal and un-ending. In his couplet he states that for as long as humanity exists, so does this sonnet. And if this sonnet exists then so does she and all her wonder.