Create a mound of dirt where you want to place the stairs, if there is not already a naturally occurring mound. The dirt should be firm, ideally containing clay; you should not use light soil. Pile the dirt up as high as you want the stairs to be and pack the dirt firmly with the back side of the shovel.
Dig the shape of the stairs into the mound and pat them with the back of the shovel to make firm steps.
Set the flat rocks on top of the individual steps. Push the rocks into the earth using your heel.
Sprinkle the moss seed around the rocks and lightly water the seeded area on a daily basis until the moss begins to sprout.