A decimal number has a decimal point.  Everything to the left of the decimal point is the integer part of the number, and everything to the right of the decimal point is the decimal part.  

The integer part of the number is divided up into units, 10s, 100s and 1000s (as for integers).

The decimal part is divided into `frac(1)(10)`, `frac(1)(100)`, `frac(1)(1000)`, with each new column (working to the right) being 10 times smaller than the previous column.

In the example above, 135.792 is made up from:

1 is 1 x 100 = 100

3 is 3 x 10 = 30

5 has a value of 5

(decimal point)

7 is 7 x `frac(1)(10)` = 0.7 (`frac(7)(10)` as a fraction)

9 is 9 x `frac(1)(100)` = 0.09 (`frac(9)(100)`)

2 is 2 x `frac(1)(1000)` = 0.002 (`frac(2)(1000)`, or `frac(1)(500)`)

The number of digits to the right of the decimal point is the number of decimal places. In the example above, the number has three decimal places.