Here's how it works:
* Schwa is a vowel sound represented by the symbol ə. It's a very short and unstressed sound, similar to the "uh" sound in "about".
* In "character", the stress falls on the second syllable, "rac". This makes the first syllable "char" unstressed, giving the "a" a schwa sound.
So, the pronunciation of "character" is roughly: ˈkær.ɪk.tər.