Read from terminal without waiting for [ENTER]

I'm sorry to bother you with such silly questions, but I recently started working with the Linux terminal and when I was reading a paper about the command stty I found the following question: > ¿How can you change the echo and read without waiting for ENTER (simply by entering a hexadecimal digit from "0" to "f")? I know that the first part stty -echo and stty echo. But I have no clue of how to do read from terminal without waiting for ENTER. I have been searching in the man the second one and I cannot find in the command stty the settings to make this posible. I know it should be something simple but I can't find a solution or logic to the addition of entering a hexadecimal digit.