If you count how many red squares there are, you can find the fraction of red squares. So 4 squares out of 10 are red. The fraction is 4⁄10
What fraction of squares aren’t red? Count how many there are. 6 squares are not red, so therefore that is 6⁄10 of the squares.
Instead of counting the squares, you could use your subtraction knowledge to work it out.
If there are 10 squares in total and 4 are red, there must be 6 squares that aren’t.
10 - 4 = 6. So as a fraction that is 6⁄10