Your init file stores Emacs Lisp customizations that should run when Emacs starts. Keep small changes in your init file and move larger code into packages or separate files as the configuration grows.

• Learn where Emacs looks with The Emacs Initialization File.
• Set variables with Easy Customization Interface.
• Save custom options with Saving Customizations.
• Use file-local and directory-local settings with File Variables and Per-Directory Local Variables.
• Put early startup changes in The Early Init File.

The Variable Index is useful when you know a variable name.