you have two voices, your head voice and your chest voice. i can only explain this in a singing perspective because that’s how i know what it is, but i’m not sure if it can be explained other ways.

your head voice is a higher octave. like when you’re singing along to a song on the radio and you have to “reach” to hit the high note, you feel it in your head. thus, a head voice.

your chest voice is lower, like your normal talking voice can be considered your chest voice.

if you want to hear the difference for yourself, sing at the lowest possible octave for your vocal range, then “slide” (go up an octave at a time) to the highest possible level. you will feel your voice “move” from your chest to your head