Emacs doesn’t need any presentation. Emacs is a software “Lisp Machine” that provides a programmable text editor, email reader, text web browser, image viwer, calculator, shell, games, easter-eggs and more. Emacs is programmed in Elisp, an Emacs own lisp dialect that is based on MacLisp, one of oldest lisp dialects, older than Common Lisp and Scheme, created in MIT. Emacs was written in 1976 by the legendary Richard Stallman. Despite many incompatibilities with Common Lisp it has many constructs similar to it and n excellent book about Common Lisp that is also useful to understand Elisp and Scheme is On Lisp - by Paul Graham. The user configuration file, which is executed when Emacs starts, is stored in the directory ~/.emacs.d/init.el or ~/.emacs. The first one is better because it is in the same directory of all emacs configuration files.