Global search-and-replace operations are not needed as often in Emacs as
they are in other editors, but they are available. In addition to the
simple replace-string command which is like that found in most
editors, there is a query-replace command which asks you, for each
occurrence of a pattern, whether to replace it.
The replace commands all replace one string (or regexp) with one
replacement string. It is possible to perform several replacements in
parallel using the command expand-region-abbrevs. See Expanding Abbrevs.