High frequency trading has increased tremendously in the last decade. High frequency trading is frequently being blamed for the flash crashes in the market. However there is also an argument that high frequency trading has helped make the market more liquid and reduced the spreads. Watch the video that explains how high frequency trading works.
https://www.youtube.com/watch?v=f2cbylOElm0
This 1 hour video explains everything that you need to know about high frequency trading!
This video also tries to explain what is HFT!
https://www.youtube.com/watch?v=GAGaReF9LaI
This is another good video that explains high frequency trading!
This video explains how high frequency trading causes flash crashes in the market!
This video explains the advantages being enjoyed by High Frequency Traders!
https://www.youtube.com/watch?v=aNoNdN66Q5E
This is another video on HFT in action!