Most of the operators we are interested in take two operands. In each of the following examples the operator has two operands:

However, unary operators take just one operand:

A binary operator will always have exactly two operands. However, sometimes one or both operands of a binary operator is a subexpression.

Sometimes a subexpression is a constant, like "8". Any expression can be a subexpression of a larger expression. In the following, both operands of the red operator are subexpressions.

When an expression is evaluated, the subexpressions must be evaluated first before the operator that joins them can be applied.

Gotcha: a subexpression may call for integer arithmetic, even though the larger expression calls for floating point. (I keep stressing this, but that is because people get caught by this all the time.)