Technically speaking what the c command does is delete and —INSERT—

Another way to you'll see the command described is as change(replace)

By itself the c command doesn't do anything. It requires a "motion"

c + →

For example, if you hit c and then the right arrow key, it will delete the character where you had your cursor on and put you in Insert mode from that point.

Note: It's almost like the lowercase i command (without deleting), if you're in the middle of a word, it will insert chars that are before the cursor.

c + ←

You can also do c and then left arrow

Note: This is kind of and sort of like the lowercase a command. If you're in the middle of a word, it will delete the character thats to the left of where the cursors was at, and then it will insert chars that are before the cursor.

** I know this sound confusing, but compare the differences where your cursor lands after doing these two commands.*

Other motions with c

c + b

This will delete the previous word, and put you in insert from that point.

Note: I will only delete a whole word, if you are at the beginning of a particular word. If you your say in the middle of a word, it will delete only the from the point of the cursor the the beginning of the word.

c + w

This will delete the word you are at, if the cursor is at the beginning of the word. If not, it will just delete to the end for the word.

c + c

This will delete a whole line

c + up arrow

This will delete the line you're on plus one more up