Assume that a one-way Hash function is secure and the best way to attack it is by using the brute force attack. It produces an $m$-bit output. Finding a message that hashes to a given hash value would require hashing **$2^m$ random messages**. Finding two messages that hash to the same value would only require hashing **$2^{\frac{m}{2}}$ random messages.**

I know only about birthday paradox involving 23 people. How do I relate the birthday paradox with this attack?