The one thing to know about WordPress
The plugin route matters here more than on any other platform. Installing from the WordPress.org repository means the widget updates through the dashboard with everything else, rather than sitting as a snippet in a template nobody remembers editing.
Where reviews belong in a WordPress site
A Custom HTML block inside a post or page, a sidebar widget area, or the footer for something site-wide. Page builders each have their own embed element.
Full-width sections suit carousel and grid layouts; sidebars and narrow columns suit a badge. Floating badges can be restricted to particular pages and to desktop or mobile.
Reviews and search results
The widget outputs review schema markup automatically. Whether Google shows a star rating depends on what the reviews are attached to — worth reading before you expect stars, because for a business reviewing itself the answer is usually no.
What does help either way: reviews on the page are content, and a page that answers what customers actually say is a page people stay on.