“When you play two separate frequencies in each ear, say 140 Hz and 149 Hz, the difference in frequency is 9 Hz. Your brain compensates for this difference, and a third tone of 9 Hz is experienced,” says Niraj Naik, founder of Trpynaural, a resource for binaural tracks. “This will result in your brain being raised or lowered and tuned into the desired frequency. This is how binaural beats are produced.”
Many people experienced in using alpha brainwave entrainment report that the state of mind associated with alpha waves is a time when they feel most consciously connected to their subconscious mind. The intense experience of hypnagogic sleep, reported by some people as a feeling of being awake and asleep at the same time, is also associated with alpha brainwaves.
Each of us is unique, and what works well for me might be totally useless to you. Generically speaking, there are three types of meditation techniques. There are techniques that take your awareness outwards, techniques that take your awareness inwards, and techniques that do a little of both. People with exceptionally busy minds tend to do better with techniques that take awareness outwards since their minds naturally head that direction anyway. People with more contemplative natures tend to do better with techniques that take you inwards. The combination techniques are a “maybe” for just about anyone, but are usually best used when a person has some experience with meditation under their belt.
Delta brainwaves have the slowest frequencies, ranging between 0.1 and 4 hertz, and these are the brainwave states associated with deep sleep, trance states, and unconsciousness. Few people can remain awake during delta brainwaves states, although this state is recorded in awake infants between ages of three months and one year and also in babies just before birth. Delta waves are also linked with increased production of HGH, DHEA, and the neuro-transmitter serotonin.
By exposing an individual to repeatedly external stimulus which can be flashing lights and/or recurring sounds, the entrainment process consists in pushing the brain to adjust to match the frequency provided. Unlike other forms of neurotherapy which require the individual to actively respond to stimulus, entrainment creates an immediate neurophysical response which is instinctive and effortless for the person being provided with the light and/or sound combinations. The key outcome of the sensory stimulation is known as the ‘Frequency Following Response’.
Your brain cells reset their sodium & potassium ratios when the brain is in Theta state. The sodium & potassium levels are involved in osmosis which is the chemical process that transports chemicals into and out of your brain cells. After an extended period in the Beta state the ratio between potassium and sodium is out of balance. This the main cause of what is known as "mental fatigue". A brief period in Theta (about 5 - 15min) can restore the ratio to normal resulting in mental refreshment.  
Binaural beats were the first method discovered for brainwave entrainment and works by delivering tones of different audible frequencies to the two ears with the difference in frequency between the two tones being the frequency of entrainment. The difference in frequency between the two tones must be less than 30 hertz, and this resulting frequency is called a beat or the target frequency, and it is processed in a brain region called the olivary body. When listening to such tones with stereo headphones, the two hemispheres of the brain become synchronized at the target frequency.
No, it isn’t, at least not in the way these people are thinking. Neither would any other entrainment product you could purchase for that matter. Part of the problem is the proliferation of utter nonsense about brainwave entrainment one can read all over the internet. There is one site in particular that comes to mind, and the contents of that site are often copied by other websites. It is a list of Hz frequencies with their corresponding (alleged) physical effects. The list runs on for many pages. I won’t bother with the link because you can Google it and find it for yourself if you feel the need for a good laugh, but here are some examples regarding meditation and brainwave entrainment from this site:
A more extensive study of over 100 participants who were undergoing general anesthesia for a day procedure, reported a decrease in pre-operative anxiety. The participants in this study listened to 30 minutes of binaural beats before surgery, but the researchers noted that people experiencing high levels of pre-operative anxiety could listen to binaural beats for up to 1 hour before anesthesia to reduce levels of anxiety.
When you hit a tuning fork, tuned to a particular sound frequency such as the note B, and hold it close to the strings of a guitar, you will notice that the B string on the guitar will vibrate because it has entrained on to the same frequency of the tuning fork. Interesting enough, the other strings will not vibrate. Only the one with the same tuning as the tuning fork.
The Frequency following response (FFR), also referred to as Frequency Following Potential (FFP), is a specific response to hearing sound and music, by which neural oscillations adjust their frequency to match the rhythm of auditory stimuli. The use of sound with intent to influence cortical brainwave frequency is called auditory driving,[39][40] by which frequency of neural oscillation is 'driven' to entrain with that of the rhythm of a sound source.[41][42]