Hi Sneha,
Thanks for the nice words and apologies for the late response.
Adobe Analytics report suites as data sources are auto created in audience manager in respect report suites mapped to an organization. You can create a cross device data source of your own and create profile merge rules.
Data sources in audience manger are namespaces that helps you organize your data.You can create your own data source depending on the use case in audience manager to store traits and segments.The users in those traits and segments will be tied to the data source Id in which they were created.You need n't necessarily use analytics data source for creating profile merge rule.You can create a cross device data source of your own and use it in profile merge rule.
Thanks,
Shweta