This manual is intended to help organizing an (international) online hackathon for junior corders and provides best practices and resources. It was developed as a result of an Erasmus+ co-funded project "Hack4theFuture of Europe" in which three programming schools from Germany, Greece and Portugal organized such an event for their participants and alumni. The aim of the project was to provide the learners a platform to work in international teams on innovative ideas while learning entrepreneurial and applying their digital skills. The project was divided into two phases: 1) the organization and execution of the hackathon and 2) the organization and execution of a subsequent project phase to further develop the ideas generated. Finally, a closing event took place.