When you prepare your application, there are certain tasks that need to be performed before the application can be submitted. For this, the system provides a checklist of these tasks. Once you resolve a task, make sure to update their status from the Tasks menu.
This way, you can make sure that you have uploaded all the necessary documents.
Besides, without resolving all the tasks (uploading all the required documents) you will not be able to submit your application.
For more information please watch the step-by-step video guide for the application.