Okay kiddo, so you know how when you're singing "do, re, mi, fa, so, la, ti, do", sometimes you want to make your music sound really pretty and fancy? One way to do that is by adding something called a French sixth chord.
Now, remember how we usually end our songs on the "do" note, making them sound complete? Well, the French sixth chord likes to trick our ears a little bit by sneaking in a note that isn't usually there, called the "augmented sixth" (that's just a fancy way of saying "it's a note that's been changed to sound weird on purpose").
So, when we play this French sixth chord, we take the note right before "do" (which is "ti"), and change it so it sounds different. Then we add two more notes to complete the fancy chord. This helps to make our music sound more interesting and exciting.
Does that make sense, kiddo? Just remember, the French sixth chord is like a special trick we use in music to make it sound really pretty!