Assuming you have already added a contact to your list, the next step is to click the "Share Task" check box. Your task is now being shared with that person.
Note: If you have not yet added your own name and email address to the sharing screen in th preferences, you will see an intramediat step the first time you share a task. It will prompt you for your own name and email address. We only collect this information to personalize the email that the person receives when a task is shared with them. We also use this information to keep track of everyones tasks on the system so we know who to update when a task is completed.