Conclusions usually

• Summarize the argument (especially in longer pieces of writing)
  
• “Bookend” a story that started in the introduction
  
• Include an emotional appeal, with which you (explicitly or implicitly) connect the “logic” of the argument to a more passionate reason intended to sway the reader
  
• Issue a call to action
  

Ideally, a conclusion will work in tandem with an introduction, having some kind of “call back” element to remind your reader of the powerful opening you provided. Additional advice for conclusions is found in the following video.