When you're assigned a to-do, the item will appear within your To-Dos area and on the appropriate date in the Calendar, and you will receive notification with a link via email, as well. The link will take you directly into the to-do item in a screen like the following.
Here you have the option of accepting or declining the assignment by clicking either Accept or Decline.
An email notification of whether you accepted or declined will then be sent back to the original assigner to update that person on the change of the to-do item's status.
If you declined the To-Do, the person who requested your assistance will receive an email notification, and the To-Do will be moved from that person's To-Dos Managing area and moved into his or her To-Dos list.
If you accepted, the person who assigned the to-do will be able to see the progress that you report on the To-Dos Managing section of his or her My Insight. When you are ready to update the completion of a to-do, click to edit icon next to Percent Complete.
You will have the option to update the completion percentage as well as the actual start and end dates.