Presenters have to read, understand, and present the paper. You also have to lead the class discussion following your presentation. You want to do two things: (1) give a concise presentation of the material in the paper (2) evaluate the contributions of the paper. Please be prepared to give a 20 minute presentation with about 5 minutes of discussion, which you have to lead.
You probably end up reading the paper several times. While you want to be critical of the material presented in the papers, you want to give a fair presentation of its contents. Attempt to be an advocate of the authors. If portions of the paper do not come to you, feel free to contact the lead author. They will be thrilled about your inquiry, because there is nothing like knowing that people actually read your papers. More likely than not, they will be more than happy to explain things to you and provide you with additional materials. So please start on your papers early, so as to get the chance to contact authors. Hey, you may decide to go to grad-school to study with them!
For your presentations, please make slides of figures in the paper, from the authors web-sites, or to demonstrate software that you may have acquired from them. Don't forget to leave ample time for discussion, which may take place during your presentation or afterwards. If you have questions about your presentation, please get in touch with me. While I am not an advocate of PowerPoint presentations, they are a tremendous help in focusing your thoughts on what to present.
Finally, provide me with a draft of your presentation at least 24 hours before you give it.