Click "Add New" and then choose "Activity"
For more information, please read How do I create an Activity?.
Click the "Select" button next to the type of activity you want to select it
Choose your activity title, class, and due date, then click "Save"
Click "Add Clipped Text"
Select the "Assignment" and source
Click to highlight the items to add
Click "Add Selected to Activity"
when you've finished adding to the activity.