Overall, very good! Your english is very clear. The things I fixed below are mostly to make things flow better, which is something that many native English speakers need help with as well. Great job! :)

Just as books nourish our mind, so do technologies improve our lives. Among the great factors which influence me, I strongly state that people now are more happy and more satisfied with their lives than people were in the past. There are two conspicuous aspects that I hold as my reasons. (This last sentence sounds a little unnatural. I would say something like "There are two primary reasons for this phenomenon.")

The first reason for my stand stance is that through the world changing, recreation in people's lives is more and more important. For example, when my father was a child, he had to study all day, because the harder he studied, the more money he would earn. Nevertheless, people now ("today" might be better.) do not think so. We emphasize doing sport playing sports, taking a travel traveling, and playing, not only studying. People know it is important to take a rest after a hard working day. People get happier and more satisfied through these recreations. (A more natural way to say this would be "These activities make people happier and more satisfied overall.")

The second reason which can be perceived by every individual is that since medical care improvement, people become happier. Nowadays, we have excellent medical care. People can get treatment and be cured when they face disease. Thus, people have longer life expectancy. Many People have more time to chase their dreams, unlike people in the past, who have had to work for their full life entire lives. More people enjoy traveling the world or learn other skills after they retired retire. The main reason is that medical care get more and more improvement ("As medical care improves more and more"), people live longer and longer. For example, my grandfather learns learned English and traveled around the world after he retired. And he said that he is really satisfied with his life now.

As we all know, there are two sides to every story. Therefore, sometimes people would be unhappy and unsatisfied. For example, people might think there is more stress since due to the quickly changing world; (Can't use a semicolon here. Use a comma.) people might want more and more things when they have money. (I would say "and having money just makes some people greedier") Nevertheless, from this these two main reasons that I presented above, I still believe that people now are happier and more satisfied with their lives now.