If you are interested in really learning more, I’d highly recommend this book, as it breaks down 91/135/121 rules and explains them really well.
No bullshit, this thing is excellent. I still routinely refer to it for 135 stuff.
Everything Explained for the Professional Pilot.
They wouldn’t have offered you the position if you didn’t meet their minimums, and they didn’t think you could be trained to meet their qualifications. Be confident, and get past that notion.
They will have their own SOP’s, so maybe you can ask them to provide some study materials. Odds are good they’ll be driven by:
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%20135-15.pdf
Sounds like you’ll be doing 135 and this will be your first turbine aircraft. Some great general and specific information in here:
https://www.amazon.com/Everything-Explained-Professional-Pilot-12th/dp/0974261300
Then this dull read to fill in the gaps
Turns out I can't read I still recommend these books though.