240113_Tour through PROPEL-V2 - one of the first boards of the structured Design Reviews, so a good example for the big picture of the docs you need to create.
240109_PROPEL_STAC_panel_photos.pptx - photos of the bare boards received back from Sierra
It's recommended to not dive into Altium schematic right now. First, skim through the next two sections of this Test Board Flow page (PartSync and Spatial Fit Planning). However, if you are itching to dive into learning Altium, "Starting at the end" is one way to learn the nitty-gritty of pushing buttons in the Altium GUI. This doc on checking for correctness of another completed board, GPS, is helpful in learning the Altium interface. It also gives extensive detail on what to look for in the native Altium files of a finished board: