Ka opens the consonant half of the varnamala and heads the first of the five vargas, the classes of five stops that form the core of the table. It is voiceless and unaspirated, made by closing the back of the tongue against the soft palate, and its class stands first because the whole consonant series is arranged by the place of the closure, running from the furthest back point in the mouth forwards to the lips.
The Sanskrit phoneticians named the class kanthya, from the word for throat, the same term they applied to the vowel a. Like every consonant sign in Devanagari the letter carries an inherent short a, so it is read ka rather than k, and a writer who needs the bare consonant adds a small stroke beneath it called the virama.
In practice a bare consonant inside a word is not written that way at all but is joined to the following consonant into a conjunct, a single compound sign in which one or both of the parts may be reduced. Ka is involved in one of the best known of those: with the retroflex sibilant it forms a conjunct so distinctive that it is often taught as though it were a letter in its own right, and it appears at the head of the alphabet chart in many schoolbooks for that reason. The form of the letter descends through the Nagari and Siddhamatrika hands from a Brahmi original of the same value, a line of descent that Richard Salomon's guide to Indian epigraphy traces through the inscriptional record.