A Powerpoint template includes a number of behind-the-scenes Layout Slides that determine the placement and format of all slide elements (font-sizes, colours, background, images, etc). When you insert a new slide into the presentation you can choose which Layout Slide to base it on:

• In the Home tab, Slides group, click the New Slide text button to expand a drop-down menu displaying icons of the available Layout Slides.
• Click a Layout Slide icon to insert a new slide based on that layout. The new slide will be inserted after the currently displayed slide.