"write this decimal in standard form"

This is a 10x10 grid of squares. So there are 10*10 = 100 little squares. The shaded in little squares represent the decimal portion. If you only shaded exactly one little square, then the value would be 0.01

If you shaded in 8 squares then you'd have the value 0.08

In this case, we have 4 full columns of squares shaded plus 2 extra. The four columns represent 4*10 = 40 squares. So a total of 40+2 = 42 squares are shaded. If you are skeptical of this claim, one way to confirm it is to count out all of the squares. It is a tedious method but it will get the job done. The multiplication method is much faster.

So we have 42 shaded in little squares out of 100 total. This means we have the fraction 42/100 which turns into the decimal form 0.42

So the decimal represented is 0.42