You can create a new Task through any of these methods...
Clicking on the Search bar at the top right corner of Scratchpad and then selecting "Create New Task"
Using Command+J and then selecting "Create New Task"
Navigating to the Task Manager and selecting "Add Task"
To complete a Task...
Navigate to the Task Manager and either...
Click the circle on the left side of the task
Click on your Task to open up the details and then either...
Click the circle
Change the Task "Status" to Completed
To add task fields...
While viewing an existing task or creating a new task navigate to the top right corner and click "Fields".