Some of the flatter fieldstone can be used either set in soil or sand or mortared on top of concrete, depending on the thickness. Then a rise for each step can be made out of the same stone you would use for walls. We sell stepping stone boulders specifically for that purpose. You can set these directly on top of each other using the thickness of the stone as a riser. They define a boundary between two areas such as turf and plant beds or plant beds and walkways.
Walls can be any height and are built two ways.
For small walls or borders, you can use stacking stone. You need to break the joints-a brick layers term meaning to cover where the stones put up against each other in a previous row to be crossed over by the current row. In some cases it may be necessary to place stones a few layers deep. Keep in mind that vertical thickness can vary according to the look you want. Larger, thicker, pieces are more stable and add height quickly but can be heavy and cumbersome to maneuver.