As Venki pointed out, there is standard business logic that will default the appropriate source, channel, and channel type when a ticket is created.
When you create a ticket via the UI, it will default the source to "Manual Data Entry". Channel typically gets defaulted when the source has multiple channels such as social, SMS, and email, where the channel defines a specific account (inbound SMS phone numbers, inbound email addresses, and inbound social media accounts). Channel Type is specific for social where not only is there a social media account, but also different social media networks such as Facebook, Twitter, YouTube, etc...