Its manner of articulation is occlusive, which means it is produced by obstructing airflow in the vocal tract. Because the consonant is also nasal, the blocked airflow is redirected through the nose.
Its place of articulation is retroflex, which prototypically means it is articulated subapical (with the tip of the tongue curled up), but more generally, it means that it is postalveolar without being palatalized. That is, besides the prototypical subapical articulation, the tongue can be apical (pointed) or, in some fricatives, laminal (flat).
Its phonation is voiceless, which means it is produced without vibrations of the vocal cords.
It is a nasal consonant, which means air is allowed to escape through the nose, either exclusively (nasal stops) or in addition to through the mouth.
It is a central consonant, which means it is produced by directing the airstream along the center of the tongue, rather than to the sides.
This sound is extremely rare and has been documented in very few languages. Most instances are found in highly specialized phonetic contexts or as allophonic variants.
References
↑ UCLA Working Papers in Phonetics, vol. 53–55, p. 212.