Where can I find the subnet mask?

Excuse me, could you please elaborate on how I might locate the subnet mask? I'm currently navigating through my network settings but seem to be having difficulty pinpointing the exact location. I've heard it's a crucial component in network configuration, yet I'm not entirely sure where to start looking. Could you guide me through the steps, perhaps highlighting the key areas I should be focusing on? Additionally, if there are any common mistakes or pitfalls I should avoid during this process, I'd greatly appreciate your insights. Thank you for your assistance in this matter.