There might have been instructions once upon a time... but they may have disappeared into the ether... I think the only ones left are on the Priorities Tab which more or less align with CG in the core book, ie steps 1-9, then go through the tabs in turn.
Typically grey boxes with thick black outlines are meant to be filled in (when they turn blue so you can see them more easily) and yellow boxes require player input of values. Eventually the plan was to lock the file so only these could be manipulated so feel free to lock it if it helps? I could probably add these basic instructions in somewhere in the next revision...
I could rename the Priorities Tab to 'start here' or something if that would help? There will always be some manual filling in of the sheet with gear, spells etc as that's where my excel skills fail

I've never used Chummer myself, but in the past I found that similar programs were great but didn't offer the rules summaries I've tried to attach to each spell, piece of gear etc. As my knowledge isn't encyclopaedic I found myself missing lots of good stuff just because I forgot about them!
And at the end of the day it's set up for me to use, if it's helpful to others brilliant