The main subject of this final thesis is the indepth description of Ruby on Rails web application framework along with the Devise gem installation and implementation process. Devise gem is a system which is used to authenticate standard users and users with different user roles within Rails applications. Besides that, the way of authenticating users with social network and other system accounts using OmniAuth is also described. What is more, thesis gives insight into basic principles of buliding web applications, such as MVC and REST architecture. Data management with Rails and purpose of Rails router are explained in detail as well. As for the practical part of the thesis, application called AlumniETFOS was built in a way that it contains all the above mentioned technologies. Application consists of two main parts, part that is used by ordinary users and the second part, used by admins. Users can browse static pages that hold information about AMA association or check news pages with posts related to it. Moreover, users have a possibility to register and log into the system. Users are able to register by submitting a required form data or with their Facebook accounts. For usual registration process, application uses Devise while OmniAuth is in charge of Facebook authentication. Logged in users can edit their personal information so admins can have insight into all current members. Admins are also allowed to delete users and edit the news page using simple CMS built into the application. Besides Ruby programming language and Ruby on Rails framework, technologies such as HTML, CSS, Sass and JavaScript make this application complete. When it comes to Ruby gems, Devise and OmniAuth for Facebook are the most significant ones, but gems for easier content representation and image manipulation, are also important part of this application.