Adding testimonials is super simple, make sure you have the Fancy Testimonials plugin installed. 

1. If you have the plugin activated, you should see a new menu called testimonials in your dashboard. 
2. Click the testimonials menu > add new, fill the content, and hit publish button.

Few things to keep in mind:

1. Name of the person, should go in post title. 
2. Testimonial should go in description area. 
3. Author image in featured image.

Quick Note: You can change the number of testimonials and background image from Live customizer (Dashboard > Appearance > Customize).