About Integers
Imagine the number line you have seen in the applet before.
We call the numbers to the left of zero negative numbers and attach a "-" sign to them. The numbers to the right of zero are then the positive numbers. Those are the numbers, that you already know and which you use e.g. for counting. We give them a "+" sign, but mostly we will not write down that sign to keep things shorter.
The set of negative and positive numbers are called the Integers.
The distance to zero of an integer is called absolute value and it is always positive. (because distances are always positive)
For example: The absolute value of 4 is 4 and the absolute value of -3 is 3.