The formula for the area of a circle is:

$\text{Area} = \pi * \text{(Radius)}^{2}$

The radius is the distance from the center of the circle to the edge:

In this problem we have been given the diameter of the circle. The diameter is the distance from one edge of the circle to the opposite edge:

The diameter of a circle is always twice as long as the radius

In this problem, the diameter of the circle is $1$

$\text{Radius} = \dfrac{\text{Diameter}}{\text{2}}$

$\text{Radius} = \dfrac{1}{2}$

$\text{Radius} = 0.5$

To find the area of the circle, square the radius:

$\left(0.5\right)^{2} = 0.25$

Now multiply by $\pi$. The number $\pi$ is approximately equal to 3.14.

$\text{Area} = \pi * \text{(Radius)}^{2}$

$\text{Area} = 3.14 * 0.25$

$\text{Area} = 0.79$