In any essay, the conclusion is a rewording and summarizing of the main points of an essay. After all, what an essay is composed up is basically a general statement with opinions, or points about the statement supported with reasons and examples. Since the word essay (derived from French) means to try, the writer tries to prove his/her point. In writing a paragraph, the same principle applies, just in a lesser dimension.
So, once the body of the essay/paragraph is written and the opinions/points are supported/proved, the writer looks back at them and writes a summary. In other words, the writer tells the reader what he/she has just told them.
Using one of the strong examples of the post above that the lion is important to the balance of nature in Africa, let's suppose you have made the point that the lion kills the weak or sickly of a herd which helps to strengthen the herds, ensuring that future generations will survive. Without the lion's killings, the herd's weak would reproduce more weak; then, the herd would all become weak, and eventually die off. Now, in the conclusion, you will summarize this point by writing that the lion ensures that only the strong of a herd surivive for future generations.
For more help see the site below which gives directives on writing a conclusion.