To delete one character, position the cursor over the character to be deleted and type x . The x command also deletes the space the character occupied—when a letter is removed from the middle of a word, the remaining letters will close up, leaving n
You can simply press the backspace key, but a useful trick to know is ctrl-o where you can run 1 command-mode command and then immediately return to insert ...
TABLE 4.2 vi Commands to Delete Text ; x. Deletes one character (under the cursor) ; X. Deletes one character (behind the cursor) ; dd. Deletes the ...