If we add one to any natural number we get the immediate successor of that natural number.
Ex: If we add 1 to a given natural number 5 then we get the next natural number i.e. 6.

The distance between any two consecutive numbers is 1 unit. So the distance between number 2 and 7 is 5 units.

Whole numbers start with 0 and continue with counting numbers{1, 2, 3, .....}. Numbers {1, 2, 3, ....} are natural numbers so if we include 0 with natural numbers they form the set of whole numbers.

In this hypothetical universe, each number is represented by dots such that the number of dots in that universe corresponds to the value of the number it represents in this universe. 
Hence, to represent two, we use two dots. When we join two dots by a straight line, we get a line segment and nothing else, as shown.

Numbers 4, 9, 16  can form squares as they are perfect squares of 2, 3 and 4 respectively.

The natural numbers start with 1. So 1 does not have any predecessor which lie under the natural numbers.

When we add any two natural numbers, the answer is always a natural number.
For example: Take any two natural numbers say 5 and 7. Add them 5 + 7 = 12, 12 is also a natural number.

We get the predecessor of any number by reducing 1 from that number. The predecessor of 1 is 0 and 0 lies in the number system of whole numbers.

The sum of any two natural numbers is always greater than any of the addends individually.

For example. 4 + 5 = 9,  9 is greater than 4 as well as 5.