Adding a Negative Number to another Number
This is like subtraction. For example...
$$6 + (-4) = 6 - 4 = 2$$
NOTE: A negative number added to another negative is always negative.
Subtracting a Negative Number from another Number
This is like addition. For example...
$$6 - (-4) = 6 + 4 = 10$$
Note: a negative subtracted from a negative can result in either a negative number, zero, or a positive number.
Multiplying Negative Numbers
If you multiply a positive number and a negative number together, the result is negative. If you multiply two negative numbers together, the result is positive. Shit makes no sense but that's the way it goes.
$$-5 \times 4=-20$$
$$-10 \times -3=30$$
$$6 - (-4) = 6 + 4 = 10$$
Dividing Negative Numbers
This is very similar to multiplication. A negative and a positive equal a negative. Two negatives equal a positive.
$$-10 \div 2=-5$$
$$-15 \div -3=5$$