To add contacts to the organization you can do it inf 2 different ways
From The Contact Module
1. Click on the "Contact"
2. Click on "Edit" icon
3. Select the "Organization" from the list
4. Click on the "Update Changes"
From The Organization Module
1. Click on the "Organization"
2. Click on the "Cog"
3. Select "Edit Info"
4. Click on "Owner and Members"
5. Select the "Contact(s)" that form part of the "Organization"
Select the contacts that form part of this organization.