It's called the primary dune. The windward side of the primary dune is steeper and is called the foredune. This is the side that the wind blows against so that the sand doesn't have a chance to accumulate. The leeward side is sheltered from the wind and sand has the opportunity to build up there. These dunes are smaller in size and their sides aren't as steep.
Dunes constantly change if there is nothing to prevent the wind from moving the sand around.
The wind doesn't stop moving sand once a dune is formed. If no plants grow on the primary dune, then the wind will remove the sand and deposit it onto the secondary dune until pretty soon there is nothing left of the primary dune. When nothing hold the dune system in place, the dunes move or migrate toward the land. Plants are the primary way dunes are stabilized. Vegetation, such as beach grass, dusty miller, beach peas, and seaside goldenrod keeps the sand in place with their extensive root systems.