In order to create a new Testimonial it is necessary to go to Testimonials in the dashboard menu => Add New.
In the image below you can see all the fields available for a Testimonial post:

You may also categorize your Testimonials:

After you added your Testimonials, you may now begin to use them on your site. Testimonials can be added to any Page by using the Testimonials shortcode. When editing a Page in visual mode editor, you will notice an icon below that is used to generate the shortcode:

When clicking on that icon a shortcode generator will appear in a popup window. You will have the option to select the categories and the number of Testimonials you want to display within your Page:

The generated shortcode will look like this:

[flo_testimonials categories='categ-1,categ-2' nr_posts='8']

The end result will be a slider with Testimonials as shown in our Demo Website.