Delete last character (delete-backward-char).
Kill last word (backward-kill-word).
Kill to beginning of sentence (backward-kill-sentence).
The DEL character (delete-backward-char) is the most
important correction command. When used among graphic (self-inserting)
characters, it can be thought of as canceling the last character typed.
When your mistake is longer than a couple of characters, it might be more convenient to use M-DEL or C-x DEL. M-DEL kills back to the start of the last word, and C-x DEL kills back to the start of the last sentence. C-x DEL is particularly useful when you are thinking of what to write as you type it, in case you change your mind about phrasing. M-DEL and C-x DEL save the killed text for C-y and M-y to retrieve. See Yanking.
M-DEL is often useful even when you have typed only a few characters wrong, if you know you are confused in your typing and aren’t sure exactly what you typed. At such a time, you cannot correct with DEL except by looking at the screen to see what you did. It requires less thought to kill the whole word and start over.