The theme has built in support and styling for the Shopify Product Reviews app right out of the box. Once installed take the following steps to display it on your product page and product cards.
1. Go to Online Store > Themes > Customize > Products > default product.
2. Click the Add section button and select the Product reviews app block.
3. Under the Product information section click Add block and select Product rating.
Go to Online Store > Themes > Customize > Theme Settings (paintbrush icon) > Product cards > Show rating.