Draw the shape of the object on your paper. Scale doesn't matter as long as you know the original measurements of the sides.
Note the length of the object next to the appropriate side of the object.
Note the width of the object next to the appropriate side of the object. The length and the width vary depending on the shape of the figure.
Multiply the length by the width. Write this number in the center of your figure. This is the area of the figure.