The conclusion should usually be slightly less than the introduction, so no more than 10% of the word count. The conclusion should be a summary of what you have written and possibly include recommendations for future research. There should certainly be no new ideas or information at this stage.
What you say in your conclusion should match what you said when you introduced the essay; it should be a restatement (but not a mere repetition) of your thesis, ideally in a way that shows more fully and clearly what you have been arguing.
Some essay briefs ask for extra information in the conclusion. You might be asked to include some reflection on what you have learnt from the research for the essay or from the module as a whole. It is important that you understand what is required in the assignment.
Remember: do not allow a strong essay to die through a weak conclusion. End with a definite statement as this will be the last thing your tutor will read.