You have to put a letter indicating the type of rhyme on each line of the poem.
The rhyme scheme of the poem "Ode to the West Wind" by Percy Shelley is the following:
-A
-B
-A
-B
-C
-B
-C
-D
-C
-D
-E
-D
-E
-E
So, the rhyme scheme is ABAB CBCD CDED EE
When you want to determine the rhyme scheme of any poem, you should look only at the final word in each line. Based on that, you will know which lines rhyme, and which don't.
Shelley’s poem has a particular rhyme scheme with is playing with the idea of the wind, of moving along with the rhymes (this is why there are three rhymes with “lay”, “Thou”, etc.)