Rhyme is so familiar I haven't included a lecture. Just be sure you understand a few basic concepts:

Of course a lot of poems rhyme. Rhyme is part of the element of sound that's so important. Rhyme can give a poem cohesion and structure, besides being pleasing to the ear.

In traditional poetry, rhyme was much more important than it is in modern poetry. Today, poets use a range of possibility, from a fixed pattern of rhyme to occasional rhymes to no rhyme at all. Sometimes the rhyme is internal: words within a line rhyme. Whatever the pattern or lack thereof, it's all part of making the poem sound good.

In order to figure out how rhyme works in a poem, and what it does for the poem, we use a series of letters to mark the rhymes. Here's an example:

The outlook wasn't brilliant for the Mudville Nine that day;	A
The score stood four to two with but an inning left to play.	A
A straggling few got up to go, leaving there the rest	B
With the hope that springs eternal within the human breast.	B
For they thought, "If only Casey could get a whack at that!"	C
They'd put up even money now, with Casey at the bat.	C

Here, day and play rhyme, and we call this first rhyme "A." The next rhyme, rest and breast, we call "B", and so on.

Identifying the rhyme scheme is easy enough. The next step is more important: asking why the poet might have chosen such a scheme. In other words, what does the rhyme scheme (or lack thereof) contribute to the poem? What does it add to the poem's overall effect and message?

In this case, the AABBCC rhyme scheme is the kind we associate with playground rhymes and kids' chants, so it's perfect for a humorous poem about baseball. In other poems, the rhyme scheme will serve different purposes, according to the poem's overall intention.