The value of the first progress indicator is set to 20, whereas the second progress indicator is set to 70. This denotes that the 20% and 70% job is done respectively. As and when you progress with the task, you can just increment the value to have the visual indication of the progress in the UI, with the ProgressBar control.
For the third ProgressBar control, in the preceding example, it's a bit different. When you are unsure about the total job to be done, you can set its IsIndeterminate property to True, as shown in the preceding screenshot. When your job is done, you can stop the indeterminate state and set its Value to 100.