Design templates are the fancy backgrounds you may have seen on other presentations. Generally, you want to use the same design for all of the slides in your presentation.
By clicking on the Design Ribbon, and moving your mouse over the different images in the Themes Group, you will see what that design would look like on your slides. Click on the design image to actually apply it.
Click on the More icon to see other options. If you don’t like any of the designs, you can just change the background color by clicking on Format Background.
Once you’ve chosen a general look from the Themes Group, you can customize it further by using built-in color or font schemes (the Colors and Fonts icons next to the theme images).
To change the background, click on the Background Styles icon, or for more control, click on the Expand icon in the Background Group (or choose the Format Background… option in the Background Styles dialog box).
In the Format Background dialog box, you can choose a solid or gradient as your background as well as a picture or texture. Note that if you close the dialog box, the changes will happen only on the selected slides. To change all slides (including ones that aren’t made yet), click on the Apply to All button.
To hide the default graphic, check the box that says Hide background graphics either in the Format Background dialog box or in the Design Ribbon.