Land and Sea Breezes MET
Land and sea breezes form when there is a slack pressure gradient, meaning that the wind is not really moving and temperature differences (ideally helped by clear skies) can start to play a part.
By day, the land warms up more than sea. The air rises, and air flows in from the sea (a sea breeze) to replace it. By night, the land cools rapidly; the air over the sea is now warmer, and rises. The air from the land flows to replace it (a land breeze.)
Sea breezes tend to be stronger owing to a greater temperature variation by day.
To answer the recent "runway" questions, think about where the runway is in relation to you and then think about which way the sea breeze will be when you turn final. If nothing else, it will be coming from the same direction as the runway was when you were downwind.