From the Google Play description:
Binaural beats work by playing tones of slightly different frequencies into each ear. To be effective, they should be used with headphones and played just above audible volume. The idea is that a beating effect will be created inside the brain due to the difference in frequencies and the brain will synchronize with this frequency. For the effect to work properly, the subject needs to relax and let go while still maintaining a state of alertness. Sleeping with binaural beats can also be useful.
Features: Sampled flowing water background loop Pink noise channel background option Configurable mixer volume for each channel To access additional features, press the menu button on your phone.