Ga is the third cell of the velar row, the voiced counterpart of Ka. Voicing means that the vocal folds are vibrating during the closure, and it is the second of the two dimensions along which the Indian analysis sorts the stops, the first being aspiration. The two dimensions together produce four kinds of stop at each point in the mouth: voiceless plain, voiceless aspirated, voiced plain, voiced aspirated. Ga is the third of those four, and its place in the row is fixed by that scheme rather than by frequency or by shape. The arrangement is a genuine phonetic classification and one that modern description has largely confirmed, which is why the varnamala is still taught as a working chart rather than only as a historical curiosity.
In writing, Ga behaves as every consonant sign in Ranjana does: it carries the inherent short a unless a vowel mark says otherwise, it hangs from the head stroke, and it may combine with a following consonant into a joined form when no vowel comes between them. Its shape, like every shape in the script, belongs to the Kathmandu Valley rather than to the inherited order it fills. Voicing is also the dimension that a reader of a Latin alphabet already understands without having been taught it, since the difference between p and b, t and d, k and g is exactly this. What the Indian chart adds is the insistence that voicing and aspiration are independent, which produces four cells where a European alphabet expects two, and it is the second dimension rather than the first that a learner has to be shown.