I have the app "Meditation Studio" which consists of some softly-spoken people talking you through breathing exercises and relaxation - would recommend for anyone wanting to try these techniques.
The problem is that understanding it rests on something most people have never even heard of, much less looked into themselves: that experience does not actually work how they think it does. Experience seems panoramic, i.e. continuously seeing, continuously hearing, etc. But that's not the way it actually is. Experience actually consists of a very rapid series of micro-messages from the sense bases, and those are stitched together by the mind to provide the illusion of panoramic awareness.
Once that's understood, you can give the real definition of mindfulness: remembering to know what kind of message the mind is currently knowing. This will be like watching attention flicker between knowing information about touching, seeing, hearing, etc. A person is being mindful when they're watching how mind's attention is moving.