I struggle to keep focused. I know many students do and sometimes they even have disabilities that make it much harder and almost impossible to study. I used 2 different apps to keep me on tasks for two weeks while studying for my exams. I used the app "Tide" as for the first week, and "Focus Keeper" the second week. Both are available on the app store and are free to use.
Tide was probably my favorite app. It was helpful and kept me focused. I think the best part was the sounds it used. I love the sound of rain on the roof when its pouring and they had a very peaceful version of that.
This was focus keeper. It was helpful but didn't use white noise.