You have put so much work into your essay that I have to reply!
I like your introduction. It's short and clear.
Many people seem to have different meaning of happiness and even though the theorists still can not define the fix meaning of it. This essay will show what happiness is to me.
With some small changes:
People seem to have many different meanings for happiness. Even theorists still can not define it. This essay will show what happiness is to me.
Paragraph 2 (I think) is about joy and feelings. Paragraph 3 is about health and physical comfort. It often doesn't matter how you organize - there is no right and wrong way. But the important thing is to organize. I might have put playing sport (paragraph 2) in with Paragraph 3 - the pleasure of good health. It doesn't really matter, as long as it is logically organized. See the IELTS descriptors for Task 2 Writing, under the heading Coherence and Cohesion, regarding logical organization.
This is a fragment, not a sentence.
For instance, playing sport, going shopping, listening to music, writing a book, practicing arts and so on.
It needs a subject or a main verb, or it needs to be joined to another sentence
For instance, playing sport, going shopping, listening to music, writing a book, and practicing arts can all give us intense pleasure. OR
Activities such as playing sport, going shopping, listening to music, writing a book, practicing arts and other amusements can be very rewarding and pleasurable.
Word Choice/Word Form
Avoid "etc", "and so on" - either don't use a list or else think of another example. Make it easy for the reader. Specify. Don't leave them guessing what "and so on" could be.
- That is a tragedy human experience.==> That is a tragic human experience. OR: That is a human tragedy.
- define the fix meaning of it ==> a fixed meaning for it.
- We should try to maintain to meet our own pleasance.
Unclear. Pleasance is an archaic word (no longer used).
We can be happy by staying healthy and doing the things we love.
One sentence, one idea
Millions of civil were killed every year by mortal deceases and a large sum of money were spent on curing and doing research.
This sentence has two ideas. Separate them. Is the second one relevant to the topic?
- Millions of people die from diseases.
- Large sums of money are spent on medical treatment and research.
Paragraph 3 might be rewritten as follows
In addition, physical pleasure and health are also an important part of happiness. Every year, millions of people die from disease. That is a tragic human experience. We cannot be happy if we suffer from any kind of illness. People should appreciate their health and learn to use their bodies.
(Some people might disagree with you here - is it possible to be sick but happy? Can even terminally-ill people know happiness?)
Overall, you seem to be working very hard to convey meaning in each sentence. I would suggest putting the dictionary away until AFTER you finish writing, and only using it to check meanings and spellings. Just try to write as simply as you can!