auto-insert-mode is an interactive autoloaded compiled Lisp function in `autoinsert.el'.

(auto-insert-mode &optional ARG)

Toggle Auto-insert mode, a global minor mode.
With a prefix argument ARG, enable Auto-insert mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.

When Auto-insert mode is enabled, when new files are created you can
insert a template for the file depending on the mode of the buffer.