To replace one word in the current line with another:
This replaces the first instance of the word "that" in the current line with the word "which".
To replace every instance of one word in the current line with another:
This replaces every occurrence of the word "destroy" with the word "delete" in the current line.
To replace every occurence of a word throughout the file, with another:
This replaces every occurence of "insert" with "add".
To interactively replace every occurence of a word throughout the file, with another:
:g/in conjunction with/s//with/gc option used in conjunction with the ls command ^^^^^^^^^^^^^^^^^^
This displays the first line containing an occurence of the pattern "in conjunction with", and identifies this occurence by underlining each character with a ^ (caret).
Entering y (yes) replaces this instance of "in conjunction with" by "with" and proceeds on to the next.
Pressing <RETURN> leaves this instance unchanged and proceeds to the next.