Mind is like a radio with six stations. It tunes into one station at a given time and that changes at a very rapid speed. The six receivers of the radio that receive the signals are like the six senses. The physical structure of the radio is like the brain. The radio signal that connects the receiver and generate the sound is like the consciousness.
In mindfulness meditation it is like tuning into one station at a time. For example, in breath meditation, we try to tune into the body and the sensation of breath. This connects mainly to the perception signal and that generates a thought about the breath (long or short). This is one of the circuits of breath meditation. If one tunes in well that person may be in a good state of concentration called "Samadhi". If one tunes out of it and tunes into the mind station fully (without having received any signals from the other five stations) this could be a like a higher state of mental absorption called "Jhana".
In insight meditation (Vipassana) one is fully aware that only one station works at a given time. Whatever the station one tunes in, the person sees the true nature of it (impermanence, suffering and non-self) and tunes out of it. Then the person awaits for the next signal to arise and fall away from the next station.
Unfortunately this is an old manual radio and therefore has no preset buttons like the modern ones. Therefore only way one can tune in and out is by practice and only by practice. There are no short cuts.