As I have mentioned above there are giant differences between the UK application, which is called UCAS, and the USA application, which is called the Common App. The difference is in what they are asking you to write about in the personal statement essays. The UK application is strictly academic, asking which major (course) you plan to study, your background in that subject in high school, and your plans for the future. These essays usually always include a discussion of books they have read in their intended major, teachers who inspired them, classes which advanced their learning, summer school classes which were helpful, or even internships.
However, the USA application essays are the opposite. None of the questions ask you to identify which major you intend to study or ask you to explain your classes in high school. The US universities really want to see that a student has done community service during their time in high school or middle school. They really want to see that students have participated in school activities, but also done some things which are paid work or volunteer work, for example tutoring children, help clean up parks, groups to protect the environment or help old people in your neighborhood, and many other possibilities.
Although the UK universities do not focus heavily on activities, both US and UK universities are very eager to admit students who have helped their community and participated in activities, not the students who have only gone to classes.