I assume dnd is no notification or signal? I have had this since high school (15 years I guess)? At the time phones weren't allowed so every day my phone had to

I assume dnd is no notification or signal? I have had this since high school (15 years I guess)? At the time phones weren't allowed so every day my phone had to be on silent and I never turned it off. I started working and phones weren't allowed. Then college and phones weren't allowed. I don't even know what my ring tone is and I only assume my alert messages work because my phone can play music...