Chandaḥśāstra

 Although not all Sanskrit literature is poetry, a substantial portion of it is, from the Vedas to the epic poems to the works of poets like Kālidāsa. Just as the study of Sanskrit itself became increasingly systematic and comprehensive, so too did the study of the form of Sanskrit poetry become more complete.

Almost all Sanskrit poetry is based on following a certain meter, or arrangement of syllables. Prosody (Sanskrit chandas) is the study of meter. But before we begin, we must first understand how meter influences Sanskrit poetry and how meter first came about. To do so, we must start with the Vedas.

As you may know by now, the Vedas are the oldest Sanskrit texts. One of their many themes is the power of both speech and the poets who have mastered speech. Given this, we can understand why the ancient Indians placed such importance on preserving the Vedas as precisely as possible: speech was powerful, and holy speech deserved to be preserved exactly as it was first said.

With this in mind, the ancient Indians began devising ways to preserve the Vedas exactly. Plain memorization could never be enough, for distortions inevitably slip in. Instead, they eventually realized that a rigorous description of the form of the poems would help preserve their shape over time. This description evolved into the formal study of meter. Both meter and the study of meter are called chandas.

But even though the study of meter is much simpler than the study of grammar, the metric form of the Vedas was not preserved well. By rigorously applying the rules of sandhi where they should not have been applied, the ancient Indians changed the shape of the meter and, by extension, the hymns themselves. But that is a discussion for another time.

Unlike the grammatical tradition, which became very complex, the metrical tradition was quite simple. We are quite sure that there were older works on Vedic meter, but none of them have survived. Indeed, one of the oldest authors we have on record, by name of Piṅgala, talks about both Vedic and Classical meter, meaning that he likely lived some time after Pāṇini. His Chandaḥśāstra, literally "the rules of meter," is almost certainly part of a longer tradition. Unfortunately, most of that tradition is lost to us today.

 Some basics

The fundamental unit of a poetic composition is the akṣara, or syllable. Several akṣaras are arranged into a pāda, or line, with fixed length. pādas are arranged into a group called a vṛtta, or stanza. Together, these vṛttas form an actual Sanskrit work.
Moving on

With all of that said, feel free to proceed to the next lesson, which introduces a common method for describing different meters.

Source

learnsanskrit.org