When viewing an individual dataset, the Topic Explorer will appear in a panel on the left, and the individual records from a search or selected topic box(es) will appear in a panel on the right.
To view the records that constitute a single topic box, left click on a topic cluster. (Hovering will also allow you to see the labels and other metrics depending on the heat map chosen.) The results panel on the right will populate with the results from that cluster. Notice the selected cluster will now be outlined in green and the Filter Topics button will now be active.