When a negative is subtracted from, it means that it would add to the negative, an example of this would be -2 - 3 = (-5), a example is when a negative number, a good way to look at it is a ladder, from -10 to 10 (i will write an example shortly) then you can make it in jumps, i realise it might not make sense in words so the following image is what it looks like:
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 -I----I---I---I---I---I---I---I---I---I---I--I--I--I--I--I--I--I--I--I---I
you can use this to make negatives easier