This video, titled "Graduated Bob," was released by "lesson cut."

The long angled bob is one of the most popular bob styles for short hairstyles.
The first step in the cutting process is to cut the back inner portion in an upside down v shape, making sure both sides are the same length.
Then cut the sides at a slant, angling down towards the front of the body.
It's a lot easier to understand by watching than by reading, so be sure to check out the video if you want to see how it's done!