The document discusses using stacks to evaluate mathematical expressions in postfix notation. It explains that postfix notation writes operators after operands, popping two elements to perform binary operations before pushing the result back to the stack. The key steps are to push operands to the stack in order, pop the top two elements to perform operations based on precedence levels from PEMDAS, and push results back to the stack until a single value remains. Resources for further information on postfix notation and stack implementation are also provided.