Process automation deals with runbooks. You can see all of it in this pane:

You could add your (existing) runbook manually or using the gallery:

As you can see, a runbook could be created in two ways: using a text editor or a graphical editor for setting up the basic structure:

It could be a PowerShell workflow, too. If you have your existing workflows from Orchestrator or anything else, you just could add them with minor modifications.

If you choose a gallery, you will have to choose the gallery target first:

This could be either PowerShell Gallery or the Script Center:

As you can see, there are different basic scripts that could be added and used directly or with small modifications:

If you will not be using a runbook, you could even use DSC for this. This means that you could set up DCS nodes (responsible for DSC) in Azure or on premises in Azure Stack. This is where all automation finally becomes hybrid:

As you can see, each VM (in Azure or on premises) is supported as a DSC node unless it is a Linux VM, as this is currently unsupported.