If you have a partner school you are at a good point!
So next step is to work with your partner school. You can do it via email or you may try to use the "My class" tool for sharing major steps with your class and with your partner school. The aim is to have 1 single file that will then be uploaded on the website.
Once you have finished your masterpiece you can proceed as follows:
1) Pre-registrer to the Inter-school competition. (if you havent' already). This means that you are the project coordinator and you will have to provide details for both schools.
2) Register your project on this page: http://www.consumerclassroom.eu/create-new-inter-school-project
3) Start filling the fields. In the second step remember to mark the button where you say that you wish to collaborate with an other school;
4) Enter details for the other school;
5) Upload the file yor students did with the other school.