1. Read all the symbols from left to right of the postfix expression
2. If the reading symbol is $operand$ then push into the stack
3. If the reading symbol is $operator$, then perform two pop operations, do the arithmetic operation and again pushed the resultant into the stack
4. finally, perform a pop operation and print the popped value as the final result.
Time complexity of evaluation algorithm is $O(n)$ where n is the number of characters in input expression.