This graduation thesis describes the process of plugin development for e-learning system called Moodle. The chosen type of the plugin is called Moodle block. The block has the function of representing results of HTML code input. Process of developing the plugin is part of learning content in Moodle course called PHP programming, placed on Moodle sites of Faculty of Science in Split, Croatia. The learning content includes lessons about introduction in PHP programming language, essential for developing plugins of Moodle system. All learning content and supporting activities are made by ADDIE model of instructional design.