Sandy,
The approval task does not show up as an option under task tab as it needs to be associated with a document(s). So in order to do what you would like to do you need to select the document that needs to be approved then right click and select approve. This will allow you to create the approval task. Once you have added the approval task then you can go to the task tab add the condition to the approval task.
If you have any other questions please feel free to email me at leslie.martensen@sap.com
Leslie