What is the purpose of the network mask?

Could you elaborate on the significance and purpose of the network mask in the context of networking and particularly in relation to IP addressing? I'm curious to understand how it aids in identifying the network portion of an IP address and how it plays a crucial role in determining the range of IP addresses that belong to a specific network segment. What are the practical implications of configuring the network mask correctly, and what challenges might arise if it's misconfigured?