For serious academic or business presentations, it is important to be transparent about your sources for factual information. You should provide citations for your sources within the visible body of your presentation. There are two common methods used to create citations for use within PowerPoint.
Use your industry standard style while creating citations for footnotes, end notes and works-cited slides. Every field has its own style conventions; for instance, the sciences tend to use APA, while lawyers use "The Bluebook." Following these style guides is important for a successful presentation.
Choose between footnotes and end notes. If you have noticed that others in your field favor one over the other, follow their lead; if no such convention exists, it is only important to be consistent and use one or the other.
Insert a text box (Insert>Text Box) at the bottom of a slide to create footnote citations. Link information (such as a book citation or a URL) to the text of your presentation by a symbol (Insert>Symbol) or number (such as [1.]), making sure the symbol or number match the citation in the text box.
Create a slide at the end of the presentation for end notes. Label the slide "Notes" and link the citation information to your body text via numbers, which are easier to organize in end notes than symbols.
Create a works-cited slide as the last slide of your presentation. Whether you've selected footnotes or end notes, always include a list of at least the most important sources for your presentation. You can leave this slide up as you begin to discuss your presentation with the audience, leaving the (correct) impression that your presentation has been well-researched.
For maximum transparency, footnotes are preferable within PowerPoint presentations. They appear longer on the screen than a single end notes page, and are therefore easier for your audience to absorb. If you do use end notes, give your audience a moment to peruse them, and be willing to return to the page if someone asks for a source.