A contact is a person or organisation, and can be added to a tenant or an owner or a contractor.

If an email address is added, the Send Email button will be enabled so you can quickly send an email to that person or organisation.

If a mobile phone number is added, the Send message button will be enabled so you can send a message to this persons mobile phone.

For each tenant or owner or contractor, one contact can be marked as the primary contact.  These details will be used when sending emails to the owner or tenant.  Also some reports only print the primary contact details.  If a second contact is marked as the primary contact, the previous primary contact will automatically be changed to no longer be the primary contact.