and different people have different opinion about being happy
-> different opinions
I believe that we will be happier by making other people happy because we can get these things.
-> we can make more relationships
by them; therefore we will be happy
-> by them. Therefore, we will be happy
He is really bad at math at first. Therefore, I often helped him with mathematic
-> at first so I often helped him wiht mathematic
Do not use one word in many times in a paragraph, it will make the reader feel bored.