Just like the PowerPoint desktop app, PowerPoint for the web lets you create designer slides quickly.
To start, select an option:
Select New blank presentation to create a presentation from scratch.
Select one of the themes.
Select a Recent doc.
Add and format text. Then select it and choose ways to change it including Font, Font size, Bold, Italic, Underline, ...
At any time, you can find new designs for your slides. They may appear automatically on the right-hand side, or see them by selecting Design > Design Ideas.