Two negatives do not equal a positive when adding. If you're in debt and you add more debt, does that get you out of debt?
Two negatives do equal a positive when you're multiplying them together though. This makes sense if you imagine multiplication as squishing or stretching a particular number on the number line. For example, imagine multiplying 2 x 1/2 as squishing the number 2 two times closer to 0. When you multiply 2 by a negative number, say, -1, you squish it so far down that you flip it to the negative side of the number line, bringing it to -2. You can imagine a similar thing happening if you multiply a number like -4 by -2. You squish -4 down to zero, and then flip it to the positive side and stretch it by a factor of 2, bringing it to 8.