Not much of this era is known. All that is known is that during this time is when the Jedi Order is first created.

What is known of this era is mostly Legends. In the Legends video games, the main source of Legends  information, we see constant wars between the Jedi Order and the Sith, which canonologically form in this era. In this era, we also see the Jedi Order established in the Republic.

The "golden age" of the Republic's expansion, when Pathfinder teams lead explorations into the farther reaches of the galaxy to expand the galaxy. This is mostly presented in the Star Wars: The High Republic book series. Phase 2 comes first on the timeline, during the Forever War between Eiram and E'ronoh. In this time phase, we see the discover and introduction of the Nameless to the universe, and the Path of the Open Hand, led by the Mother, on a mission to 

During this era, Rey establishes a new Jedi Order preceding from the original that fell a long time before and that also presides from Luke Skywalker's attempt to rebuild. Not much more is known except for this.