How do Headlands and Bays form on a coastline?

There are a number of ways where coastlines see the formation of headlands and bays but there are a number of factors which must be seen for these to form.

Firstly the geology and lithology of the coastline is very important. Geology is the different types of rock that we see and lithology is the patterns and distribution of this rock. 

The most common way we see headlands and bays is on a discordant coastline, where the rocks are distributed alternate resistant and then less resistant rock as if in a stripy pattern with the bands of rock pointing towards the see rather than flat up against it (this is known as concordant).

Secondly for headlands and bays to form there will be a prevailing wind in the direction of the rock meaning there is sufficient wave energy to erode the cliff to make this formation. 

As the waves hit the cliff they erode the material through hydraulic action (sheer force of the waves) and abrasion (the sediment in the water breaks down the cliff material like sand paper). This means that the less resistant rock erodes at a greater rate to the more resistant rock and consequently the less resistant bands retreat to form sheltered bays leaving the more resistant rock as protruding headlands.