You can open the YouTube export dialog via one of the following methods:
Click the Save Video drop down button. Select the YouTube option.
Click the Save Video... menu item and in the wizard that opens, select the Upload, then the YouTube option.
Once reaching the YouTube export dialog, you can choose assorted settings that will be applied to the exported project.
After making your selections click on Create, to being the export and upload process.
If required the YouTube Authorization dialog will appear. Login to your YouTube Account, and follow the prompts to allow the application to access your online profile.