Pointers needed!

Good day to you all.
I am stranger in these parts and I am looking to do some research into various historic issues regarding the RAF in WW2. I understand the PRO is the best place to go but I have been totally stumped by their website. Can I do any research online or do I have to go there?!
Appreciate you guys have been asked this loads of times but I just need pointing in the right direction and I will toddle off to do the legwork. I am also looking for anyone with information about 619 squadron RAF – on behalf of a relative.
Thanks in advance for any help! 🙂