An operator is a symbol (token) that compose an expression.
It operates on values on its side (left and/or right).
They represents a function but where the argument are on both side of it.
<MATH> ie \\ \text{ }\\ c = a + b \\ \text{ }\\ \text{is equivalent to} \\ \text{ }\\ c = f(a,b) </MATH>
This function are mathematical function (ie they return the same data type than their input)
Operators can also be seen as actions on variables and values.
Grammar - (Order of (operations|precedence)|operator precedence)
a + b
var += a
// equivalent of
var = var + a
See Assignment