Any work that you submit to your teacher should hopefully be done in your own words; at eNotes we are here to help you find your answers, and to give suggestions that will help you. I provided a link below to a really great and in-depth summary of the poem that you should take a look at; it will hopefully help you to understand it a bit better.
In a nutshell, Tennyson, in the poem, is writing from the point of view of Tithonus, the former lover of the goddess of the dawn, Aurora. Aurora has granted him the gift of eternal life, but not the gift of eternal youth, so Tithonus grows older and older, without the ability to die. Tennyson, in the poem, speaks as Tithonus might have, mourning over how lonely he feels, how he doesn't feel a part of the human community anymore ("Why should a man desire in any way/To vary from the kindly race of men"), how he misses his youth and beauty, and how immortality isn't all it's cracked up to be ("Of happy men have the power to die"). He begs the beautiful Aurora to "Let me go: take back thy gift" and allow him to be "restored...to the ground."
It is a beautifully written poem filled with longing and imagery that enhances the sad and lonely plight of Tithonus. I hope this helped!