What is a rhyme scheme?
You can work out the rhyme scheme of a poem by labelling the words that rhyme with each other. It will help you see the pattern of the poem.
For example, if a poem's first and third lines rhyme you should label those 'A'. If the second and fourth lines of the poem rhyme, label these 'B'. Then you can see your four line poem has an 'A B A B' rhyme scheme.
If all four lines rhyme with each other, this is an 'A A A A' rhyme scheme.