How does the position of a digit in a number relate to its value example with decimals

Above, we have written the number 6,702 in expanded form, or as a SUM of its different parts according to place value. 

The digit 6 in the number 6,702 actually has the value 6,000 and the digit 7 actually signifies the value 700. This is why our number system is also called a place value system, because the value of a digit (like 6 or 7 in our example)depends on its placement within the number. In other words, the digit 6 in 6702 does not mean six but six thousand, because the six is placed in the thousands' place. The place of a digit determines its value.

The comma between thousands and hundreds is added as a separator for easier reading.  In some countries an empty space is used instead: 6,702 is written as 6 702.