Operators specify the type of calculation that you want to perform on the elements of a formula. Excel follows general mathematical rules for calculations, which is Parentheses, Exponents, Multiplication and Division, and Addition and Subtraction, or the acronym PEMDAS (Please Excuse My Dear Aunt Sally). Using parentheses allows you to change that calculation order.
Types of operators. There are four different types of calculation operators: arithmetic, comparison, text concatenation, and reference.

Arithmetic operators
To perform basic mathematical operations, such as addition, subtraction, multiplication, or division; combine numbers; and produce numeric results, use the following arithmetic operators.
Arithmetic operator
Meaning
Example
+ (plus sign)
Addition
=3+3
– (minus sign)
Subtraction
Negation=3–3
=3* (asterisk)
Multiplication
=3*3
/ (forward slash)
Division
=3/3
% (percent sign)
Percent
30%
^ (caret)
Exponentiation
=3^3

Comparison operators
You can compare two values with the following operators. When two values are compared by using these operators, the result is a logical value—either TRUE or FALSE.
Comparison operator
Meaning
Example
= (equal sign)
Equal to
=A1=B1
> (greater than sign)
Greater than
=A1>B1
< (less than sign)
Less than
=A1<B1
>= (greater than or equal to sign)
Greater than or equal to
=A1>=B1
<= (less than or equal to sign)
Less than or equal to
=A1<=B1
<> (not equal to sign)
Not equal to
=A1<>B1

Text concatenation operator
Use the ampersand (&) to concatenate (join) one or more text strings to produce a single piece of text.
Text operator
Meaning
Example
& (ampersand)
Connects, or concatenates, two values to produce one continuous text value
="North"&"wind" results in "Northwind".
Where A1 holds "Last name" and B1 holds "First name", =A1&", "&B1 results in "Last name, First name". 
Reference operators
Combine ranges of cells for calculations with the following operators.
Reference operator
Meaning
Example
: (colon)
Range operator, which produces one reference to all the cells between two references, including the two references.
B5:B15
, (comma)
Union operator, which combines multiple references into one reference
=SUM(B5:B15,D5:D15)
(space)
Intersection operator, which produces one reference to cells common to the two references
B7:D7 C6:C8