Sorry, I understood your question as how to interact with an existing ProgressControl.
You'll first need to add this in your window:
code:
<Control xsi:type="ProgressControl" Id="PrgDownload">
<Postion Left="10" Top="10" Width="150" Height="25"/>
</Control>
Then, whenever you need to get or change the position, use Progress_GetPos or Progress_SetPos. Alternatively, you could first set the step increment with Progress_SetStep and then use Progress_StepIt to step further.