Here's how:

* Erosion: Waves crashing against the coastline break down rocks and cliffs, creating sand and sediment. This eroded material is then transported along the coastline by currents.

* Deposition: The transported sand and sediment are eventually deposited in calmer areas, often along the shoreline, forming beaches.

So, while erosion provides the raw materials for beaches, deposition is the process that actually builds them up.

It's important to remember that beach formation is a continuous process, constantly being shaped by the balance between erosion and deposition.