A testimonial is a short statement from a real user about their experience with a product, shown with their name and, ideally, their role or photo.
The best ones describe a specific before and after: what was hard, what changed, and a result.
Ask for them right after a user reaches a good result, and ask permission to use their name.
Why it matters for a launch
Testimonials answer the visitor's question "does it actually work for people like me?" better than any copy you write.