Negative Number Rules
Here is a little, helpful applet on the rules of negative numbers.
Negative numbers can seem peculiar on first encounter. That is true historically.
This article from Nrich gives a short summary of how negative numbers as we now know them came to be: https://nrich.maths.org/5747
This second article gives credit to some of the various cultures who are part of the negative number story: https://nrich.maths.org/5961
Thirdly, this article gives some ways to intuitively understand the arithmetic operations of negative numbers. https://nrich.maths.org/9958