1. The 'Existing Mapping' section:
The settings tab allows you to map the object name with the field name. This means that, while using the salesforce object say, the field which is mapped here will be used for sending & receiving the message.
Hence you need to carefully map the field and on the other side save the valid data on salesforce objects for that particular field.
2. The 'Update Mapping' section:
You can select more objects and map them to the related fields by choosing them from the Object Name & Fields Name drop-down list. You can provide Primary and Secondary phone values here.
After selecting the objects and the fields click on Add Row link which allows furthermore mappings to be added.
Once done, click the Save Mappings button. The confirmation message will be displayed.
To delete the mapping click on the delete icon.