40Hz binaural beats as described on the Huberman Lab podcast have been shown to be effective in increasing focus and concentration. This is partly through increases in the neurotransmitters dopamine and acetylcholine. They can be used to increase focus or concentration before focused work or other tasks you need to be focused on such as workouts in the gym. It is recommended to listen to the binaural beats before starting the task you need to focus on. However, if you are easily distracted you can also play the binaural beats throughout your focus session.

Sources:

Psychol Res, 2017 Jan.;81(1):271-277.