What is Number Line
Just imagine you start from zero and go on walking along number line in the positive direction. As far as your eyes can see, there are infinite numbers.
You might begin with picking up only natural numbers like 1, 2, 3, and so on. We denote this collection by the symbol N.
Turn back and pick up zero and put it into the bag. You now have the collection of whole numbers which is denoted by the symbol W.
Now, stretching in front of you are many, many negative integers. Put all the negative integers into your bag. It is the collection of all integers, and it is denoted by the symbol Z.
Number line is also having Rational numbers. The collection of rational numbers is denoted by Q. Rational comes from the word ratio.
There are numbers on the number line that are not rationals; called irrational numbers.