What is Rhyme Scheme, ye ask?
Rhyme scheme is the formal arrangements of lines in a stanza or poem. It is usually notated with lowercase letters of the alphabet (such as ababcdcd. . .etc), with each letter representing a different rhyme.
For instance...
The last word of the line is the most important. Since "behold" is the last word in the first line, it starts the rhyme scheme with "a". "Hang" does not rhyme with "behold", so it starts on a different rhyme, "b". But since "cold" and "behold" rhyme, they are both "a", and so on.