Whenever Richard Cory went down town, A
We people on the pavement looked at him; B
He was a gentleman from sole to crown A
Clean favored and imperially slim. B
To apply a rhyme scheme to a poem, you have to look at the last word or two words in each line of poetry.
town rhymes with crown
him rhymes with slim
This pattern is an alternating pattern.
There are couplets in which the rhyme of each two lines of verse is the same.
Let such teach others who themselves excel,
And censure freely who have written well."
There are also quatrains and tercets.
In the study of poetry, you don't really "apply" a rhyme scheme to a poem, rather your job is to identify the rhyme scheme (if there is one) and then talk about its impact. This is normally done by nominating a letter for each "rhyme" within the poem. Let's take Sonnet 116 by Shakespeare as an example (watch out for the letters at the end of the lines):
Let me not to the marriage of true minds A
Admit impediments. Love is not love
B Which alters when it alteration finds, A
Or bends with the remover to remove: B
O no! it is an ever-fixed mark C
That looks on tempests and is never shaken; D
It is the star to every wandering bark, C
Whose worth's unknown, although his height be taken. D Love's not Time's fool, though rosy lips and cheeks E
Within his bending sickle's compass come: F
Love alters not with his brief hours and weeks, E
But bears it out even to the edge of doom. F
If this be error and upon me proved, G
I never writ, nor no man ever loved. G
Therefore, with this poem, you would say that it had a regular ABABCDCDEFEFGG rhyme scheme - typical of Shakespeare and his sonnets.