Andy Puddicombe (the founder of the Headspace meditation app) gives the example of driving a car, to explain the difference between meditation and mindfulness. When you first learn to drive, you choose to drive on a quiet road, rather than a busy motorway (or highway for you Americans).
Mindfulness is about being immersed in the present moment, not thinking ahead to your amazing future or regretting things that happened in the past. It can be used in any situation. But the easiest place to learn and practice mindfulness, is during meditation, where you're sitting still and just focusing on your breath, or just focusing on one thing. Its the serene, peaceful road you can use to train your mind.
Source: The Headspace Guide to Meditation