For example: You are editing an invoice. A client calls and you need to schedule a follow-up task. Instead of having to leave the invoice, go to your task list, add the task, then find your way back to the invoice you were working on, just use the Add Item menu!
Click the white "Add Item" button toward the top-right corner of the screen.
Then, choose the item you would like to add to the system. A window will open up over what you are working on, and when you save the item you'll be taken back to the original screen.