The conclusion paragraph is almost a mirror image of your introduction:
Then, briefly sum up all the main points in your argument and "hammer home" your assertion in 3 - 5 sentences. Not too much detail is needed here.
One option is to combine this process with restating your thesis - think about it as turning your one-sentence thesis statement from the introduction into 3-5 sentences: one for the main idea, then several more for the supporting points.
Thesis statement in the introduction:
"X is very important to Y because of A, B, and C."
Restating in the conclusion:
"It is clear that Y would not be what it is without X. A is a huge factor in this. B is crucial to X's role in Y as well. Above all else, C is what really makes this connection clear."
Remember to end your conclusion paragraph strong.
Just as you want to start an essay with something to draw the reader's interest, you also want to end strong with a good clincher, or a profound statement. This sentence should make the reader think "hmmm, interesting," or " "How true!" or something along those lines.
You can think of this as answering the "so what?" question for readers. If there's anything you want readers to take away from this paper, anything you wanted them to learn, see differently, or be left thinking about, what is it?
Check out this presentation by our Writing and Grammar Tutor Claire Pienaar about how to write an introduction paragraph.
Conclusion Example from Cambridge Rindge and Latin School's "Writing a Conclusion" Tip Sheet
The problem of teen gang violence can be eliminated. It will, however, take time, money, and a combined effort on the part of many people. Organized, free, after-school programs such as: sports teams and games; art, music, and drama activities; internships in local area businesses and professional organizations; and interesting volunteer activities in the community would help engage teens in worthwhile pursuits outside of school hours. More job opportunities for teens, especially those funded by state and local programs, would offer income for teens as well as productive work for the community. Outreach to families through schools, community organizations, and places of worship would help promote inter-generational activities that could improve family closeness, helping teens to work on their problems at the family level, instead of taking them to the streets. If these programs can be implemented, we will surely see a decrease in teen gang activity and safer streets and neighbourhoods for us all.