The synagogue is a new form of communal institution according to the Oxford Companion. Whereas in the temple, sacrifice is the primary way to serve God, the synagogue uses prayer, study, and exhortation.  The service is open (nor restricted relative to inner and outer courts or with respect to Jew or Gentile) with all ceremonies in plain view. Their origins are far from clear:

Despite its importance in Jewish history, the origins of the synagogue and its early development are shrouded in mystery. Only during and after the first century ce does literary and archaeological evidence appear for Palestine. As for the Roman Diaspora, references before then are practically nonexistent (and what does exist refers to the Diaspora). Synagogue inscriptions from third- and second-century bce Egypt have been preserved, as have remains of a Delos synagogue building dating from the first century bce.

Owing to the paucity of sources, opinions have varied widely as to when, where, and why the synagogue developed. Theories have ranged from the late First Temple period (eighth-seventh century bce), through the exilic (sixth century) and postexilic (fifth century) eras, and down to the late Persian (fourth century) and Hellenistic times (third or second century). Most scholars have assumed a midway position, one that posits the emergence of the synagogue closely following the destruction of the First Temple in 587/586 bce, either during the Babylonian exile or soon after, when the Jews returned to Judea during the era of restoration.

Concerning synagogue services, Torah-reading was crucial, spread with varying practice over the Jewish year:

While Torah reading was accepted as normative on Sabbaths and holidays and later on Mondays and Thursdays as well, the division into weekly portions varied considerably. In Palestine the Torah was read over a three- or three-and-a-half-year period with a plethora of local traditions on the precise divisions of the weekly portions (141, 154, 161, 167, and 175). Moreover, the practice in Babylonian communities living in late Roman and Byzantine Palestine only added to this diversity: They concluded the Torah reading in one year. How widespread the custom was of translating the Torah portion into the vernacular is unknown, but the use of Greek in addition to Aramaic cannot be denied.