My first port of call would be to really get to grips with the Business Reports. Try not to glaze over the figures go through each of the reports and get to know them. I recommend doing a bit at a time - say 1hr per day so you don’t get overwhelmed (or bored). Once you get over the overwhelming amount of data - things will start to make sense to you - persevere and you’ll be rewarded.
Understand the figures and you’ll start to carve out a working process that works for you. Once you understand the figures things will make a lot more sense.
My next stop would be the Payments Reports - there is a wealth of information in these reports, especially the Refund reports.
I’d like to give you a blueprint but every business is different and everyone works differently.
Best to become a master of your own business and will require you to put in the hours to understand what goes on behind the scenes.
Your boss will genuinely thank you for the effort you’ve put in and you’ll be the office Amazon Master