Most people will play it as a standalone game and it's absolutely fine to do so. However, if you want to catch up on the lore, there are handy recap videos such as:
Iirc, BG3 story takes place a 100 years after BG2s story. Because of the time between them, it is very approachable as a standalone.
You can carry over story elements from your BG1 save to BG2, but not from BG1/2 to BG3.
Definitely standalone. Having some knowledge of D&D lore or Baldur's Gate lore may enhance your enjoyment but only marginally IMO.
As the others have pointed out, you can play standalone, but if you're somewhat interested, perhaps the Wikipedia page is an "ok" start: https://en.wikipedia.org/wiki/Baldur%27s_gate, looking through the references there.