Data sources are connected accounts of your external applications (that are available as integrations on Reportz)
In order to make some great reports, start with adding your preferred data source from available pool of added integrations.
You can see all currently available integrations on Reportz Integrations page .
And more are soon to come :)
Some sources require you to simply add your login data and connect your account in a few steps, while others require you to add your application token. (more on this subject here)
All added sources on your account can be reviewed and managed here, on Sources tab on Account Settings page.