mac – why does the legend or code or elements computer stuff pop up when I press increase volume?

So, I don’t know what exactly I did but all of a sudden I couldn’t hear sound through my headphones. I had checked if the volume still works and it does. It turns out the volume on my headphones was mute but that didn’t fix my problem as when i pushed the increase volume button on the keyboard a side popped up that looks like legend or code or something. None of the top row buttons work properly. Brightness doesn’t do anything. I mean when i press it the brightness doesn’t go up or down. When I press decrease volume the screen is goes to like that area where it shows you your desktops and open windows. I need help please.