What is area?
Area is the size of a surface or how much space it takes up. It is measured in units squared.
This fantastic site here gives further explanations on what are is and how to calculate the area of different shapes. There is also another useful link here which helps explain how to calculate the area of more complex shapes.
Area of a regular shape.
Area of Compound Shapes
Finding the area and perimeter of irregular shapes.
Area of Triangles: the Basics