This API allows to visualize tracking for progress of long lasting tasks.

The usual usecase goes like this:

ProgressHandle handle = ProgressHandleFactory.createHandle("My custom task");
...
// we have 100 workunits
// at this point the task appears in status bar.
handle.start(100);
...
handle.progress(10);
...
handle.progress(50);
...
// at this point the task is finished and removed from status bar
handle.finish();

There are several options on how detailed visualization you want.

task with unknown duration or with hard to show progress steps.
task with known scaled steps
task with known steps and also with a time estimate for completion

All these usecases are supported by methods of {@link org.netbeans.api.progress.ProgressHandle} class. Additionally it's possible to include textual information about current progress.
If the task allows to be cancelled by the user, then you have to implement {@link org.openide.util.Cancellable} interface and pass it to the {@link org.netbeans.api.progress.ProgressHandleFactory} when creating the handle.