Apologies in advance for what will surely sound like a, "well why can't you just Google it" question, but I'm struggling to find good literature that presents the basic construction of genus two partition functions (or honestly, really good literature on genus one partition functions). I'm looking within the context of conformal field theories, an interested in the geometric expressions, but I can not seem to find papers that aren't dense in jargon. It's not my field, so I don't know who the go-to authors here are, and I want something that doesn't just assume that I know exactly which path integral methods they mean or why a 'central charge 24 bosonic string' is something I might lose sleep over (with or without Moonshine).

I'll appreciate any recommendations/starting places.