Okay kiddo, have you ever seen a word with a little line above one of the letters? That's called a bar or a diacritic. It's like a tiny hat for letters!
Sometimes we use bars to change the sound of a letter. For example, in the word "café," the bar above the "e" tells us to say it like "eh" instead of "ee."
Other times, bars are just there to help us know how to pronounce a word. For example, in the word "māori," the bar above the "a" tells us to say it like "ah" instead of "ay."
So basically, a bar (diacritic) is like a tiny marking above a letter that helps us know how to say it. Pretty cool, huh?