Instead of typing the file path in manually, you can just drag the file onto the Terminal window. You can check the hash of your file by opening Terminal.app, typing md5 /path/to/file and pressing Enter. Before installing a BIOS file, make sure that its associated core plugin is installed and the MD5 hash is correct, or it will not work! Installing a BIOS is as simple as adding a game to OpenEmu, just drag-and-drop a BIOS onto your library! If the core you are currently trying to use needs a BIOS file, OpenEmu will alert you with a popup message. In order to emulate some systems, BIOS files are needed due to increasing complexity of the hardware and software of modern gaming consoles.
If files aren't automatically copying, that means you have incorrect files. Important: Do not manually copy a file to your BIOS folder.