When written before your paper is finished, an introduction can be uncertain, vague and unconvincing. Once you know exactly what you are introducing and how your paper has unfolded, it will be easier to write a conclusion that belongs with, and represents the argument in, your paper.
In the introduction, you tell your reader exactly what he or she can expect to find in the body of your essay, and you should think of it as a kind of contract: your reader is expecting you to do what you said you would do, and prove what you said you would prove.
You should use your introduction to provide enough context (who, what, when, etc.) for your reader to understand your thesis statement – the idea that organizes and supports the essay.
A draft of your working thesis has probably been sufficient up until the final draft of your paper. A this point, you should revise your thesis statement to fit the essay you have actually written, not the one you thought you would write at the beginning. It's completely normal that your thesis statement might change as you write, so you just have to make sure your final thesis works with your final draft.