When you enter new slides into a presentation, the default layout provides a title box and a text box that is set up as a simple bulleted list. Therefore, just creating a new slide creates a bulleted list.
You can turn off the bullets in front of any paragraphs by selecting the paragraphs and clicking the Bullets button on the Formatting toolbar to toggle the bullets off. If you want to remove the bullets from all the paragraphs (remember a text line followed by the Enter key is a paragraph), select the entire text box and click the Bullets button.
When you insert your own text boxes using the Text Box button on the Drawing toolbar, the text does not have bullets by default. You can add your own bullets by following these steps: