To show your slides FULL SCREEN you can use the SLIDESHOW BUTTON

This means that you will not see the Speaker Notes.

Speaker Notes are helpful as you can add links, extra information or hints for what you want to say for each slide when you present them.

If you want to see these, you can click the arrow beside the SLIDESHOW button and click PRESENTER VIEW. This means you will see your speaker notes (but your audience won't), they will simply see each slide full screen.