Adding two numbers means you are joining two groups.
When you add numbers, the first number
is called addend1 and the second number is called addend2 and the third number is called addend3 and so on.
The result you get is called SUM.
When you add two or more numbers you will get thesum of the numbers.
If you add a number with zero the sum will be the number itself
If the first addend and the second addend are same, then that kind of addition is called Doubles addition