An operation is a procedure which produces a new value from one or more input values.

+, - , x, are
symbols which represent the arithmetic operations of adding, subtracting,
multiplying and so on. In general, an operation is a rule for determining
the new element from one or more elements.

Some e.g. of mathematical operations are shown below :

For example, the principal square root of 9 is 3, denoted
√9 = 3,
because 32 = 3 x 3 = 9. If otherwise unqualified,
the square root of a number refers to the principal square
root: the square root of 2 is approximately 1.4142

Plus sign + means that two numbers are added together. For
example, in the picture on the right, there are 3 + 2 apples
- meaning three apples and two other apples - which is the
same as five apples, since 3 + 2 = 5

In mathematics, it is often useful to view or even define
subtraction as a kind of addition, the addition of the opposite.
We can view 7 - 3 = 4 as the sum of two terms :

Multiplication is written using the multiplication sign
x between the terms, that is, in infix notation. The result
is expressed with an equals sign.

For example, 2 x 3 = 6 (verbally, two times three equals six)