What is ActiveAdmin?
Active Admin is a Ruby on Rails plugin for generating administration sytle interfaces. The goals of this plugin are easy-to-use for non-techical users and fast for developers.

How To Use ActiveAdmin
Suppose we are create Blog web application.
$> rails new blog

Add the following to your Gemfile.
# Gemfile
gem 'activeadmin'

Run bundle install.
$> bundle install

Install ActiveAdmin.
$> rails generate active_admin:install

After installation is finished, it will create:
1. An configuration file on config/initializers/active_admin.rb
2. AdminUser model on app/models/admin_user.rb
3. An directory called app/admin to configure the admin interface of our resource.
4. Migration files.

Migrate your db and start the server.
$> rake db:migrate
$> rails server

Visit http://localhost:3000/admin and log in using:
  • Email: admin@example.com
  • Password: password

Next, create Post model.
$> rails g model Post title:string content:text

Create admin interface for Post model. Because we use ActiveAdmin, we don't need to create controller for Post model. This generator will create file on app/admin/posts.rb.
$> rails generate active_admin:resource Post

This creates a file at app/admin/posts.rb for configuring the resource.
ActiveAdmin.register Post do
index do
column :title
column :content

Visit http://localhost:3000/admin/posts to see the result.

More information about ActiveAdmin: