To open the similarity report, click the similarity icon:

Similarity score in Turmitin

A new browser tab will open containing the submission in the Turnitin Feedback Studio document viewer.

Note: Ensure your browser is set to allow popups from www.turnitin.com

To view details of text matches occurring in the document, ensure the Similarity tab is activated:

Similarity tab displaying Match score box

To view Match groups, it is already set to default on the right side beside the submitted assignment within Turnitin. They are explained also.
Match score box displaying similarity breakdown
Sources of similarity can be observed in the tab located beside Match groups. There is also a button to allow for Overlapping sources.

Source tab