The number line describes how numbers relate to one another by taking a number and placing all numbers that are larger than it to the right of it and all numbers that are smaller than it to the left. This is true for every number on the number line.
Typically a number line starts with a 0 (zero) in the middle. All numbers to the left of the 0 are negative and all numbers to the right are positive.
As can be seen above, as we go right the numbers increase. As we go left the numbers get smaller and smaller. The arrow on either side of the number line indicates the line goes on forever in both directions.
Smaller Intervals
The number line is not just limited to using integers. Each interval can be broken down into sub intervals as small as we want. For example lets say we want to break down the intervals into a value of .2 per interval. Our number line may look something like this:
As you can see we now seperate each mark by a decimal value. Number lines can also be broken down using fractions as well:
Here each interval represents 1/4.