Emacs is a text editor with commands for opening, saving, navigating, and editing text. It can be started by running "emacs" from the command line. Basic navigation uses keys like C-f to move forward a character or C-b to move backward. The cursor can be positioned with keys like C-a to go to the start of the line or M-< and M-> to go to the start or end of the document. Text can be searched using C-s followed by a pattern, and replaced using M-%. Regions of text can be copied or killed with keys like C-w and yanked back with C-y. Files can be loaded and saved using commands like C-