You might have played a game where someone said “count backwards”:
-1,-2,-3,-4,-5,-6,…
What this is saying is, if you want to add two negatives numbers, you can add the positive equivalents take that answer, put a negative sign on it and you’re done.
What is (-3)+(-4)?
3+4=7
Putting a negative on that gives -7.
(-a)(-b)=(+a)(+b)
(-a)(+b)=(+a)(-b)