Subnetting Concepts: This 1st video is just to get you oriented to why subnetting is used/needed and the "Concept" behind it...
IP Address Classes: The 3 Most Used Classes of IP Addresses and How They Are Used and Understood
AND-ing: The AND-ing process used between the Subnet Mask and the IP Address...
Variable Length Subnet Masks (VLSM): How to Use "Classless" Subnet Masks to Create More Subnets In a Range of IP Addresses
SUPERnetting: Why Do We Need SUPER-netting?
CHEAT SHEET: The Easiest Method for Solving Subnetting Questions