Our minds operate faster than our bodies, so a lot of distracting, often negative thoughts can jump in and out—a state sometimes called "monkey mind."
Mental noting is a great way to deal with monkey mind. You come up with a word or phrase that describes what you're doing. It's like a mantraA mantra is just a word or phrase you keep repeating. It monopolizes your inner speech, blocking other thoughts from creeping in. There is no magic to it, and it doesn't really matter what the word is, as long as it makes you feel comfortable. , except it changes as you change what you're doing. You can also add a soft "Yes!" after each mental note, to give yourself a nice positive reinforcement.
Mental notes anchor you in the present moment and monopolize your inner speech. Most negative thoughts are about the past or future, so if you are focused on the present, you're usually in a place that's okay If the present moment is not okay—for instance, a dentist is working on your teeth—feel free to imagine you are somewhere else!.
This isn't to say that we should never think about the future with concern and never do a post-mortem on something that went wrong in the past. But many of us overdo this, and it leads to suffering. Focusing on the present—with a feeling of loving-kindness—is an excellent way to keep yourself in balance.
If you'd like to learn more about the science behind this, please visit Deeper on Mental Noting.