Here are the steps to use the ruler guides in PowerPoint to align objects on a slide:

1. Turn on ruler guides by going to the 'View' tab and clicking on the 'Ruler' button.
2. Create guide lines by clicking and dragging the rulers on the slide canvas/work space.
3. Align objects by placing them where you would like within the ruler guide lines you have created.
4. Finally, turn off ruler guides by clicking the 'Ruler' button again.