Go to the Left Navigation Menu and click "People" to get to the People Page.
Click "Add Person" at the top right of the People Page. Two options will drop down. Choose "Add one person":
Enter the new person's first and last names on the following page. You can also add any alternative names, such as maiden names or uncommon nicknames. Click the "Create New Person" button at the bottom of the page to save your changes:
You will now land on a newly created Person Profile. If the new person has a Group, you can add it on this page as well. Be sure to update their contact info and preferences: