Suppose you enabled admin moderation for the Product Reviews add-on. In that case, all reviews submitted by customers get a pending status first and are specially marked on the Reviews page in the store's Admin area.
To moderate a pending review:
Click on the Pencil icon on the review line.
Check if the review requires editing (you can edit the review right away).
Click either Approve or Remove.
To moderate more than one review at a time:
Select the reviews from the list.
Click the Check button below the table and select the option you require from the expanded button menu:
Approve selected will approve all the selected reviews and publish them on the product details page of the respective products;
Unapprove selected will hide the selected reviews resetting their status from Published to Pending).