If, in the presence of these tones, you relax and let your mind go, your mind will naturally synchronize with the beat frequency. In this way it is possible to tune the frequency of your brain waves to particular frequencies that you have selected, using of the four bands: Delta - deep sleep, Theta - dreaming and intuitive stuff, Alpha - awake, focussed inside, Beta - awake, focussed outside.

It is also possible to produce mixtures of brain waves of different frequencies by mixing binaural tones, and in this way, with practice and experimentation, it is possible to achieve rather unusual states, such as out-of-body stuff, and more. See the books by Ken Eagle Feather, and the Monroe Institute site for more details. The Monroe Institute have apparently put 40 years of research into these techniques.