Use the figure of the first quadrant of the unit circle to find $s$ in the interval $\left[0, \frac{\pi}{2}\right]$ if $\cos s=\frac{\sqrt{2}}{2}$.

Step 1 ：Use the figure of the first quadrant of the unit circle to find $s$ in the interval $\left[0, \frac{\pi}{2}\right]$ if $\cos s=\frac{\sqrt{2}}{2}$.

Step 2 ：The cosine function gives the x-coordinate of a point on the unit circle corresponding to a given angle measured in radians.

Step 3 ：In the first quadrant of the unit circle, the cosine function is positive and decreases from 1 to 0 as the angle increases from 0 to $\frac{\pi}{2}$.

Step 4 ：The value $\frac{\sqrt{2}}{2}$ is the cosine of the angle $\frac{\pi}{4}$, so $s=\frac{\pi}{4}$.

Step 5 ：Final Answer: $s=\boxed{\frac{\pi}{4}}$