You're quite right- DM is used to publish the packages you give it, but you need some method to create and publish those to begin with.
The demo you saw probably was an example using TeamCity. We have have a plugin for this that lets you configure it to automatically publish a package to your feed on each check-in to your source control system for example.
If you're not using a build system right now, there's other ways to publish packages.
We supply a commandline tool, "RGPublish", which can package up a folder or visual studio project, another commandline called "SQLCI" which can package up a database (in combination with SQL Compare/Data Compare for flexibility) and also addins for both SSMS and Visual Studio for easy package creation.
These are documented on our website, and i'd suggest looking here
to get started.