How do you put a background on one of your slides on Libre Office powerpoint/presentation?
Another way if you’re creating a new presentation is to go File>Wizards>Presentation this will allow you to pick an overall theme for your slide show
depending on what exactly you want to do, you could create one or more additional master pages and then select the one(s) you need from the master pages menu in the task menu.
As far as I remember the guideline describes this sufficiently well.