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Understanding place value is like learning the address of each digit within a number. Each digit has a different value based on its position. This concept is fundamental in math as it helps us break down numbers to understand them better.

In the example of rounding 21,094 to the nearest thousand, we first need to spot the "thousand's place." Imagine the number is like a street where each digit lives. Starting from the right, first is unit's, then ten's, hundred's, and then thousand's. Here, the '2' is in the ten-thousands place, '1' is in the thousand's place, '0' in the hundred's place, '9' in the ten's place, and '4' in the unit's place. By pinpointing the right value, we can handle numbers more precisely.

Rounding could seem a bit mysterious, but it's just following a simple set of rules to make numbers easier to work with. When you're rounding to a certain place value, you only need to focus on the digit to the right of the place you're rounding to.

• If the digit to the immediate right of the target place is 5 or more, you bump the number up. This digit rounds up.
• If the digit next to your rounding place is less than 5, you leave the target digit as it is, or in other words, it rounds down.

In our problem with 21,094, because the '0' is less than 5, we round down, meaning the thousand's place stays '1', and the rest become zeros.

Whole numbers are the simplest kind of numbers to understand and work with. They include all natural numbers starting from 0 onwards without any fractions or decimals.

When rounding whole numbers, the process involves simplifying the number to make calculations easier while maintaining its `nearness` to the original number. In the exercise, we used whole numbers only, specifically because rounding to the nearest thousand always results in a whole number.

Rounding changes a number into a tidier whole format such as 21,000 out of 21,094, retaining its essential size and value while making it neater and easier to use.