Similar to templates and themes, built-in layouts provide heading structure and reading order for screen reader users. Inserting text boxes can cause issues with order that information is presented to screen reader users.
From the HOME tab, select New Slide.
Choose an appropriate layout and select Add Slide.
Ensure each new slide has a unique title.
NOTE: Using built-in layouts also allows you to maintain that same structure and reading order when the presentation is converted into a PDF document.