Summary of Sonnet 18 by Shakespeare.

Lines 1—4
Shall I compare thee to a summer’s day? (No), you are more lovely and more seasoned or moderate. In spring there are rough wind that spoil the blooming roses which are very Lovable. Moreover, the duration of summer is very short. (You are not comparable to a summer’s day because you are more beautiful and more seasoned; you don’t have the negative qualities that a summer’s day has.)

Lines 5—8 
In summer, sometimes the sun gives very scorching heat. Sometimes, the sun become dusky, (may be) due to the cloudy sky. All beautiful things on earth are subject to change, and they loss their beauty. They  loss beauty , sometimes, accidentally and sometimes, naturally by the law of this universe.

Lines 9—14
But your everlasting beauty will never change; the beauty that you possess will not be lost. Death will not be able to kill you and take you to the underworld because you will keep on growing in these lines. As long as man lives on the earth these verse lines will keep you alive.