Before uploading code, you will need to create a compute capsule to contain it.
After logging in, navigate to https://codeocean.com/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 see how.) You will then be taken to a new private workspace, where you can upload and run your code, configure your computational environment, and when you are ready, publish your code.