If you don't have an LLC set up, and don't have an EIN and if you are a sole proprietor you can proceed with the other "no" option shown in your screenshot.
If you scroll down in the step-by-step guide found in module 11, you will see the guide for sole-prop registration. ๐
If you DO have an LLC set up and are 100% sure that you DON'T have an EIN, you can try proceeding with the top "yes" option in your screenshot and use your SSN during the process.