I have tried correcting the grammar mistakes, no comments on the content! Hope this helps!  :)

In the modern world, young people want to become independent persons as quickly as possible. The best way to do it is to get a job. Some youth young people think that they should concentrate on studying at school. Others believe that a part-time work has many advantages. Who is right?
Personally, I agree with the people who think that the important thing at their age is studying at school. First, they do not have any free time to work. They spend it to study and learn new materials. Second, if you work when you go to school, you will receive bad marks because you cannot concentrate on 2 objects.
On the other hand, working somewhere means you begin earning. It means you are becoming independent from your parents or relatives. Moreover, if you work, you get your own experience that will help you in the future.
I cannot agree with people who think that working part time has a lot of advantages. People should not try to become independent in this age because it is not so nessecary necessary now. Also, you can get your experience when you are older.
To sum up, I would like to say that studying at school is the most important and most nessecary necessary (necessary what?). People get new knowledge, do many difficult tasks, and become smarter. All these, of course, demand concentration.