Ka is where the consonant section begins, and where the arrangement of the table becomes visible as a grid rather than a sequence. Five points of articulation run down one axis and five features across the other, and this letter sits in the first cell of both: the furthest back point in the mouth, and the plainest of the five treatments, voiceless and without aspiration. Everything else in the consonant table is described relative to positions like this one.
On the page it is an ordinary and very frequent letter, entering freely into conjuncts, taking every vowel mark and appearing in a large share of the vocabulary. Its cluster with the retroflex sibilant, which writes the sound conventionally transliterated ksh, is treated in several Indian traditions almost as a letter in its own right and is given a distinct shape that a learner has to acquire separately from either of its parts.
In East Asia the letter acquired a second life that has nothing to do with how often it occurs. It is the seed syllable of the bodhisattva known in Japan as Jizo, and it is the character most often cut in Siddham on the stone figures raised to him, which are among the most common religious objects in the Japanese landscape.