Short init.el

;; Melpa
(require 'package)
(add-to-list 'package-archives
             '("melpa" . "http://melpa.org/packages/") t)
(when (< emacs-major-version 24)
  ;; For important compatibility libraries like cl-lib
  (add-to-list 'package-archives '("gnu" . "http://elpa.gnu.org/packages/")))
(package-initialize)

(require 'helm)
(helm-mode 1)
(defun fu/helm-find-files-navigate-forward (orig-fun &rest args)
  (if (file-directory-p (helm-get-selection))
      (apply orig-fun args)
    (helm-maybe-exit-minibuffer)))
(advice-add 'helm-execute-persistent-action :around #'fu/helm-find-files-navigate-forward)
(define-key helm-find-files-map (kbd "<return>") 'helm-execute-persistent-action)
(define-key helm-find-files-map (kbd "RET") 'helm-execute-persistent-action)

(defun fu/helm-find-files-navigate-back (orig-fun &rest args)
  (if (= (length helm-pattern) (length (helm-find-files-initial-input)))
      (helm-find-files-up-one-level 1)
    (apply orig-fun args)))
(advice-add 'helm-ff-delete-char-backward :around #'fu/helm-find-files-navigate-back)