Click on "Contacts" in the menu. Then click on "New contact".
On the following page, you can enter details for the contact and also add photos and files such as the person's CV. Press "Create contact" to save.
If you go back to the first view of the contact book, you will se that the contact has been added to the list. To edit the contact, press the icon with three dots on the right and select "Edit". In this view, you can also delete the contact.