Apple logic board 820-2390 is covered by this 2.31 MB RAR archive, whose name gives no model, revision or list of contents. Unpack it to find out whether it holds a schematic, boardview or both. The 820-xxxx pattern is Apple's own logic board numbering, found printed on the PCB, and that number plus any revision should match before use. Schematic pages help trace power rails, enable lines and signal paths, while boardview files open in viewers like OpenBoardView for locating parts and test points.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @Mac_Shematic_Santale. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.