To make the stars you’ve received visible on Google, your website needs to have the right Rich Snippet markup. Your website builder will need to add this markup correctly. This markup ensures that Google can retrieve additional data from your site and enrich the search. For example:
The additional information about the review, marked with green arrow, is directly read from the source code of the Hollandbikeshop website. On the website itself, you can display that as text for example; at Hollandbikeshop, they have incorporated this into a widget they developed themselves:
It looks like any other widget, but in the source code we can see the information that Google uses to show the stars in the search results:
Google then indexes this source code like so:
You can find out how Google indexes your website at http://0.3-2e.schemaorgae.appspot.com/. This data is then used to show your reviews in Google’s search results.