Oh, ā is a letter that looks like the letter "a" but it has a line above it, just like a hat. It's called a macron.
Now, remember how when we say the letter "a", it can have different sounds in different words? For example, "cat" and "car" both start with "ca-" but they sound different, right?
Well, the letter ā sounds the same every time we read it. It sounds like the "a" in "hay" or "day".
It's a really special letter because it helps us know exactly how to say a word, so we don't get confused!