What should I put in the Task description?

Anything and everything...

The Task Description can be used in many ways. If you are assigning a task to yourself, the task description can be brief, more of a reminder of what the task is about. If you are assigning a task to someone else, the task description turns into instructions or directions for the Assignee. You can tell the Assignee exactly what needs to be done. The more detailed the task description is to an Assignee, the less likely you will be to receive clarifying questions.