The Forgotten Realms Campaign Setting is a pretty decent place to start.
The Forgotten Realms Wiki - Books, races, classes, and more and
Candlekeep are decent free resources.
Short summary (not a big fan of FR myself, so probably getting some of this wrong):
In 2E, there were the Forgotten Realms. Everyone that played it liked it.
3E came around and the mechanics changed so they had the Time of Troubles as a catastrophic event. People died. Gods died. Generally everyone was pissed for a while.
4E came around and the mechanics changed so they had the Spellplague as a catastrophic event. People died. Gods died. Generally everyone was pissed for a while.
5E will come around and the mechanics will change so they... apparently won't destroy everything. Generally everyone will probably still be pissed for a while.