Firstly, alternating bands of soft and hard rock, at right angles to coastline.
Secondly, waves erode rocks, through abrasion and hydraulic power.
Thirdly, this causes the less resistant (soft) rock to erode quicker, forming bays. However the more resistant (hard) rock to erode slower, and sit out at sea, forming headlands.
Finally, the bay is now sheltered by headlands, on either side, so sand can be deposited and beaches can form in sheltered areas.
