Use Find... (Cmd-F) to enter the string to be searched (Find string) and the string to be substituted (Replace string) for matched instances. Use checkboxes to indicate whether you want lower case and upper case characters treated as different characters (Case Sensitive), and whether you want searches limited to Whole Words.
Find Next (Cmd-G) and Find Previous (Cmd-E) will take you to string matches forward or backward in the text from the current selection or cursor position.
Replace (Cmd-=), Replace & Find Next (Cmd-H), and Replace All substitute the Replace string for the Find string instance(s). The first two of these commands are undoable. The last two commands work in the forward direction from the cursor position.
