RAR archive for the Samsung Galaxy J1, model J100MU, size 4.19 MB. The name carries only the model, so the exact contents need checking after extraction; such packages usually contain schematics or service manual pages. They help locate components, trace power-up and charging circuits and pick out test points when a phone does not boot or charge. The MU suffix marks a regional variant, so confirm it matches the phone, since other J1 versions may differ in radio and SIM circuitry.
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 @esquematicosdecelulares. 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.