Like other editors, Emacs has commands for searching for occurrences of a string. The principal search command is unusual in that it is incremental; it begins to search before you have finished typing the search string. There are also nonincremental search commands more like those of other editors.
Besides the usual
replace-string command that finds all
occurrences of one string and replaces them with another, Emacs has a fancy
replacement command called
query-replace which asks interactively
which occurrences to replace.