Decimals represent numbers between whole numbers, such as 0.1 being between 0 and 1. When adding, subtracting, multiplying, or dividing decimals, it is important to line up the decimal points before performing the calculation. For multiplication and division, the number of decimal places in the answer should match the total number from the numbers in the problem. Dividing decimals requires moving the decimal points in the divisor and dividend to properly set up the calculation.