If you are logged in, you can click the plus-sign and tell about how this dataset has been reused by filling the form that opens. After you have saved the reuse information, they will be shown to any user who clicks the button on the left. The button shows the number of reuse cases that have been reported.
This is the permanent identifier (PID) for this dataset. Use it when citing this dataset. An identifier is unique and permanent. With identifiers you can unambiguously refer to a dataset. The permanent identifiers for digital systems are analogous to the ISBN for books. Examples of identifiers for data are URN, Handle and DOI, but many others exist.