Have you read the poem? If not, I recommend it; it is very short and easy to understand. I have provided a link to it below, and encourage you to read it for yourself if you haven't already.
The main theme of this poem is springtime. It is how in the spring, the earth is given new life. New grass, flowers, birds, and new growth and beauty are all around. Hughes states that "earth puts forth new life again," and that all of the new growth-the trees, grass, birds-seem to shout "Of life, of life, of life!" Even people are impacted by nature's rebirth; "passing boys and girls go singing too," and everyone is happier and filled with rejuvenation and hope.
I hope that those thoughts help a bit; take a look at the poem itself too. Good luck!