Before uploading code, you will need to create a compute capsule to contain it, along with the data and dependencies it needs in order to run.
To do so, log in and go to your dashboard, where you will find the New Compute Capsule button. Click it and choose the appropriate language from the drop-down menu. (You can add more languages later if you need to. See Setting up additional languages on Code Ocean to find out how.) You will then be taken to a new private workspace, where you can upload your files, as well as run and publish your code!