Once you've installed Just Dance Wii 2020 WBFS, playing the game is easy:
Most players use USB Loader GX or WiiFlow to launch the WBFS file from the Homebrew Channel.
Since "Just Dance Wii 2020" is a fan-mod, it is almost never distributed as an original disc. It is distributed exclusively as a file. You cannot buy this on Amazon or eBay—you must prepare a USB drive.