To enact these changes, you should: make sure you are on the Main Slide Master (the one at the very top in the left column), then highlight the Click to edit Master title style text, click on the Home Ribbon and choose a font, size, and color from the Font Group, then click on the Slide Master Ribbon (to the left of the Home Ribbon) to return to the Slide Master View.
and once you close the master, this format will be in affect on all slides – including the ones you later add. With Slide Master, any of the formatting for your presentation can be changed at once and then applied to all slides immediately for example, you can change the font of the title or text, the type of bullets used, add an image to the background, add an image to every slide, etc. The Master is what controls how your slides will look: what fonts, colors, bullets, etc. To make changes to the format of all your slides at once, using the Slide Master is probably the best idea.
