1. Happiness is considered very important in our life. Why it is difficult to define? What factors are in achieving happiness?
Successful like usually comprises happiness which is somehow intrinsic and essential. Regarding this, some factors we can achieve exist. However, it is no doubt that happiness make us difficult to define.
Some may clearly say that anyone can succeed in his like without happiness. On the other hand. There is no exaggeration that even though of a lot of money, fame or property person has, he will never be able to refer to himself as who is about to take a step onto successful timeline unless he tend to pursue happiness.
The others would probably want to recognize what factor they can achieve. Most commonly, two significant components are necessitated in fairly better life. First of all, we should take care of family or our relatives(in case of the non-family belonged). Undoubtedly, they belong to us and have a great capability of making life abundant. Second is, living once is controlled by one who does, which we should keep in our mind, must go through enjoying itself. No one seems to (ruin-> like ruing 자체수정 :p) his life.
Despite knowing many factors to get happy and importance of happiness, we still fail to define what it is. Because this is a state of mental process. However, on the bright side, all human beings are distinctive from themselves, so it can be assumed that each person has different aspect to what extent he becomes happy. It means that being (in a status of happiness -> happy 자체수정) depends on how we realize the reality.
To sum, things including money and fame does not create advanced life but happiness and it is made of a number of factors although it is quite hard to define it. Happiness will come close to us if we call it.
I don't think this is correctable. You're trying to write sentences that are beyond your level of capability. Also, I don't think adding Korean (or any other language part from English) will help you in a IELTS test.
I would be interested in seeing a few simple correct sentences from you on the theme of happiness. What can you write correctly in English with confidence and competence?