how to write a composition

Hi everybody, I have a problem with writing
when I have a composition exam I used to memorize sentences like:
We all agree that....is important things in our life.
We owe to ....which play a role part in our life.
In my point of view, I think that .....bring all evil to our society....and so on
I have many sentences like above which my friends wrote to me. I memorize them before exam then I gather and write them in any composition with any topic.
my question, Is it right to do that?
I learn English since 3 years and I still beginner student. I can not write a composition even in my native language. I think the writing is skill and I do not have this skill.

[Mariner]

It is true, writing is a skill. But this is not something that you "either have or don't", despite what some people might think. True enough, some people might have a natural "flair" for it, but that's far from affirming that some people "simply don't have it". It's all about work and practice.

Perhaps this is something that you have heard before, but let me repeat it: Read, read, read... Read as much as you can, from newspapers to books, from funny cartoons to political analyses. The more your eyes and mind are exposed to texts, the easier it will become to express your own thoughts.