If you see this theme demo, you may be seen there is a section for clients testimonials.
You can add testimonials from the admin area. Navigate to Testimonial > Add Testimonial. Put the client name in the title box and the testimonial in the content box. Upload a featured image for the client image. At the bottom, there are two options. First one is Client Designation and another one is Company Name.
The testimonial itself will look like bellow in the front end of your site.