To add a watermark to the background of slides, you can follow these general steps using popular presentation software such as Microsoft PowerPoint or Google Slides:

1. Open your presentation software and open the slide deck where you want to add the watermark.
2. Navigate to the slide master view. In PowerPoint, you can typically find this option under the “View” tab, and in Google Slides, it may be under the “Slide” or “View” menu.
3. Once you’re in the slide master view, you’ll see a master slide or layout that controls the formatting of all the slides in your presentation. Select the master slide or the specific layout you want to modify.
4. On the master slide, insert the watermark image or text. You can typically do this by selecting the “Insert” or “Insert Image” option and choosing the desired image or text box. Position the watermark where you want it to appear on the slide.
5. Adjust the watermark’s appearance and transparency to your liking. You can typically resize, rotate, or format the watermark by selecting it and using the provided formatting options. Look for options like “Format” or “Picture Tools” to access these settings.
6. Once you’re satisfied with the watermark’s appearance, exit the slide master view and return to the normal slide view. You should now see the watermark applied to all the slides based on the master slide or layout you modified.

Note: The specific steps may vary slightly depending on the presentation software you’re using, but the general concept remains the same. Remember to save your presentation to preserve the watermark for future use.

If you’re using other presentation software or need more specific instructions, please let me know the software you’re using, and I’ll provide further guidance.