The Core of Focused Attention Training

The core of focused attention training is the ability to be aware of the mind wandering, disengage from what it wandered to and refocus back on the intended object. So when you're doing mindfulness you can generally focus on anything in the present moment and it's usually a sensation. But I guess it can also be watching your own thoughts. You'll do that or like the body scan. So what are, could you just fill that picture out or structure there? There are two different things to kind of that you can practice.