One of the most intimidating but extremely important subjects in networking is subnetting. If you are like me, you totally ignore it and put it off as much as possible. That is until I found a straight to the point video on one of my favorite e-learning sites; udemy.com.
Check out the IP Addressing and Subnetting by Sikandar Shaik. At the time of writing the video is free and if you have an account you can add it to your repository of courses. The course is broken down into 18 specific lectures over 3.5 hours of video content.