Hello,

There is two ways to look at your problem,one is internally and other is externally and both are interconnected. You have to understand what's going on in your mind regarding quality of thoughts, if it's not so good quality you'll automatically be diverted towards not so productive things. On an internal level,you can work on meditation, start with few minutes on a daily basis and then increase it afterwards, you'll see a sense of calmness within you which will increase you clarity. When the mind is chaotic, it's unable to focus so you've to recognize those activities that sap your energy, invest this energy into some productive work.

You can follow the steps mentioned below:
Don't multitask, the only way to gain focus is to be focused on one work,whatever you're doing whether it's studying or something else,just invest all your energy into that by getting rid of all distractions,focusing on one thing at a time will increase your concentration power.
Minimize the screen time, switch off from social media, gadgets if you need to be, instead cultivate new interests.
If you feel anxious about anything whether it's exam or something else,then do make it a point to discuss it out with your parents or anyone who supports you.
Lastly, don't obsess yourself over the things not in your control, as I said it'll sap all your energy, work on things that's in your hand and you've control over.

Hello,

One can't focus on the things when they are literally busy with other work or not able to concentrate due to other issues like, fun, games, friends etc.,

.Now, if you are busy with the things in your life, then start preparation only for 1 hour in a day, as the days goes on, you will yourself increase the time for preparation, as your interest increases.

.Now, if your are getting diverted with friends, games and other things. Then, first make a thing clear that, there's no value for a life without education. Make a strong aim that, you will complete the syllabus in this time, no Matter what.

.Try to watch, life stories of successful persons, their struggle, their hardwork, will inspire your making your goals strong.