Testimonials get displayed on your site wherever you add a "Testimonials" block, which can be added on any page. You must add a Testimonials block to at least one page of your site (or your testimonials won't be seen).
When you add the "Testimonials" block, you will be given some options to customize how the testimonials will be displayed, as follows:
Some display options are only available in some circumstances. For example, if you select the Slideshow display layout, then you will be provided with two additional options: one to control the slideshow Duration (how many seconds to display each testimonial before going to the next one) and slideshow Transition Effect (e.g. Fade, Slide, Wipe, Zoom, etc.).
Some sites like to display one random testimonial for each Testimonial block and they also add Testimonial blocks on various pages throughout their site. Other sites like to also have a testimonial page and to display a random 10 (or All) testimonials on that page. Others like to display a random 3 testimonials on a specific page of their site. It's up to you.
You must add at least one Testimonials block to your site, otherwise the testimonials will never be displayed.
Next Step: Read the "How do I Add a Testimonial" entry.