You may want to review adding and subtracting positive fractions first.
To add signed numbers, first you check if the two numbers have the same sign or opposite signs. If they have the same sign, then their sum also has that sign, and you can add their values to get the value of the sum. For example, −4 + (−3) = −7. If they have different signs, then the sign of the answer is the sign of whichever one is bigger. So 5 + (−4) will be positive, but 5 + (−7) will be negative. (Note that by “bigger” here we just mean that the value is bigger, ignoring the sign.) The value of the answer will be the difference of the two values. So 5 + (−4) = 1 and 5 + (−7) = −2.
To subtract signed numbers, just flip the sign of the second one and then add them. So 7 − 10 = 7 + (−10), which is −3, but 7 − (−10) = 7 + 10, which is 17.