Sea breeze consists of a lot of aspects, so we divided the development of a land breeze in 3 steps.

1.
During a hot day in the spring or summer the land warms up quicker than the sea. This happens because large amounts of water can absorb more energy without warming up. The warm air above the land rises, while the air at sea remains there.

2.
As the warm air is less dense than cool air, the air above land expands in response to the heating. This way an area of high pressure forms at higher levels above land, and an area of low pressure above the sea. This cause that air at higher levels flow offshore.

3.
At lower levels the pressure is vice versa, since the air pressure is caused by the weight of air above. Wind flows onshore at lower levels because of this phenomenon. Because the lower air above land warms up (thus rises) and upper air above sea cools down (thus goes down) the circle is complete.

Sea breezes occur at any time of the year, but are most common during fall and winter. That's when the sea is still cold from the winter, and the land is warm (especially during the afternoon).
Sea breezes are the opposite effect of land breezes.

A land breeze is the opposite from a sea breeze. Because the sea is warmer than the land, air flows offshore at lower levels and onshore at higher levels. See also: Land breezes