Tta heads the retroflex class, the third of the five, and it is made with the tip of the tongue curled back against the roof of the mouth. The Sanskrit phoneticians call the class murdhanya, which means formed at the top of the head, and the name is a description of where they located the closure rather than a metaphor.
Its place in the order follows the same rule as everything else in the consonant section. The classes run from the back of the mouth forwards, so the retroflex class stands between the palatal and the dental, and within the class this letter takes the first slot: voiceless, unaspirated, the plainest treatment of the sound.
In the vocabulary of classical Sanskrit the retroflex stops are noticeably less frequent than the dentals, and a large share of the words containing them are either borrowings, onomatopoeic, or produced by a rule from something else. That skew is one of the standing questions of Indo-Aryan linguistics, since the retroflex series has no counterpart in the languages Sanskrit is related to outside India and does have counterparts in the Dravidian languages spoken alongside it.
On the page the letter behaves ordinarily. It carries the inherent short a, takes the full range of vowel marks, and enters conjuncts freely, most often with the retroflex nasal and with the retroflex sibilant that belongs to the same articulation.