When you are editing your page or post, you will see a tool icon like this:
Clicking on the button will bring up the screen seen above.
Group – Choose which group you want to pull your testimonials from.
Limit – If you want to limit a number of testimonials to be displayed, choose a number.
Random Order – If you want to display testimonials in an random order instead of how they are ordered in the admin panel.
Use Excerpt – If enabled and an excerpt is present, a shorter version of the testimonial texts will be displayed.