The specific naming convention "2559osub" suggests a categorized backup or a "beatmap pack."
: Inside, you will likely find several .osz files (the standard format for osu! beatmaps). Installation :
: These are the individual levels or songs in the game. 2559osub.7z
If you have osu! installed, you can simply drag and drop the extracted .osz files into the game window.
: A popular rhythm game where players click circles to the beat of music. 2559osub.7z
: Ensure the download completed fully; a truncated archive will result in a "Header Error" during extraction.
: Use a tool like 7-Zip or WinRAR. Right-click the file and select "Extract here." 2559osub.7z
Alternatively, move the files into the Songs folder within your osu! installation directory.