The 'Source' field is how a guest has heard about your property. 'Reason' field is why they are staying at your property.
To add a Source field option, go to Configuration (located among the options to the left)
Under the 'Customization' section, choose 'Source of Contact and Reason for Reservation'
You will notice two tabs at the top of the screen. One for 'Sources' and one for 'Reasons'. The selected option will be highlighted in blue. In this example, 'Sources' is the current selection:
To add a new Source, choose 'Add New Referral Source' from the top right corner of the screen
Enter the label for the source (such as 'Newspaper'), select whether you want the option available on the booking engine, and then select 'Save Custom Field' from the top right corner.
To create a new 'Reason', select the 'Reasons' tab from the top of the screen:
Click on 'Add New Reason' from the top right
Enter the label (such as 'Business'), select whether you want the option available on the booking engine, and choose 'Save Reason' from the top right corner of the screen.
Source of Contact can be added to either the contact data (selecting the person from the 'People screen'), or from a reservation, in the Notes and Details section
'Reason' can only be added to the reservation screen, but is also located under the 'Notes and Details' section.