Think of the "a" in "about" or the "e" in "the". They both have that short, unstressed "uh" sound. That's a schwa!
Here's an example:
The word "about" has two syllables:
* a - This is a schwa syllable because it has the short, unstressed "uh" sound.
* bout - This is not a schwa syllable because it has the stressed vowel sound "ow".
In simple terms, a schwa syllable is like a "weak" syllable, the one that doesn't get much emphasis.