If you want to base the color off another cell's value, then you should use an absolute reference or the
Normally, we might want to color the cell itself (e.g. if the value is greater than 20). We could use a formula
=A1>20. This is a relative reference: if you applied it to several columns, then it would treat each cell as
A1 and do the comparison.
Suppose that we want to color an entire row if a value in Column B is greater than 20. In that case, we'd select the appropriate columns to apply the conditional formatting and use the formula
$B means it only looks at the value in Column B. The
1 is still relative, so it will look at each row's value in Column B.
If you wanted to do something a bit more complicated, like color a row based off a value two rows higher, then you'll need to use
ROW in your formula.