If you noticed those id="TheObjectLabel" attributes in Figures, tables and code listing you have already understood half of how cross-reference works.

Those id="something" attributes are unique labels identifying those objects. The other half of the task is understand how to use them for actual referencing.

This is done via a plain <xref linkend="TheObjectLabel"/>.

Since labels are to be UNIQUE it is adviceable to follow the guidelines provided in the relative appendix Appendix C.