How can I write a conclusion on the essay titled "Explain the Social Inequalities that Exist in our Society"?

The conclusion should recapitulate the main thesis. If you have a strong thesis and strong arguments that support your thesis, then the conclusion should show how it all fits together. You could even say something, like:

In light of the discussion, the conclusion that social inequalities should be clear for these reasons...

One mistake that I see once in a while in a conclusion is that people add something new. This is almost never a good idea, because it leaves the reader with something other than your thesis in view at the end. So, summarize.