Loads of lore at

https://forgottenrealms.fandom.com/wiki. Many google searches of locations, an event (e.g. spellplague), dates (1492 DR), key people (elminster, mystra) will get you to the appropriate page on this site with convenient cross-references as wikis excel at. Web 1.0 at its finest.

https://dndbeyond.com/sources/basic-rules/appendix-c-the-five-factions

Factions

While there are many other minor factions/organizations, the primary ones referenced in adventures of 5e are the Emerald Enclave, the Harpers, the Lord's Alliance, Order of the Gauntlet, and the Zhentarim. Premade adventures often have faction options and there's also resources on dmsguild. Faction missions/quests for members help set the tone of the worlds interplay and can give adventurers additional hooks for decision making alliances yielding benefits such as aid, resource replenishment. Characters of the world are typically aware of the existence and desires of factions whether or not they themselves are (optional) members.