Archive labelled only OPPO R15, 5.61 MB in rar format, with no hint in the name about what it holds. For this phone it may contain schematics, a board layout or service documents, so extract it and check the file types before use. Diagrams of this sort help trace power rails, charging and display circuits, while layout files need a boardview viewer to locate parts and test points. Confirm the material matches the board version in your device before relying on any value or location.
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 @SMART_PHONE_SCHEMATICS. 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.