1. While in the Philanthropies section, click on 'Activity' listed on the right side of the Philanthropy you'd like to add the Activity to.  (See item 1)
  2. Click on the 'Add Activity' button on the right top corner. (See item 2)
  3. Enter the name of the new activity. (See item 3)
  4. Click on the 'Add New Activity' button to complete the process. (See item 4)