To add a text box in PowerPoint, follow these steps:

1. Open PowerPoint and select the slide you want to add the text box.
2. Select the 'Insert' tab at the top of the page.
3. Scroll through the 'Text' options tab and select the 'Text box'.
4. After selecting the 'Text box', click on the slide where you want the box to appear.
5. Once on the slide, update the text box by typing in your text.
6. If needed, you can customize your text box by changing the font size, color, or font type.