Method #1 of adding a slide
Take note that if for example you selected slide number 2 and then followed the steps above, the new slide will be added after slide number 2. However, if you placed your cursor before slide 2, the new slide will be added before slide 2.
Method #2 of adding slides
Method #3 of adding slides
Method #4 of adding a slide
In the notes page view, click the new slide button on the formatting toolbar (Automatically, the new slide will be added after the existing slide).