From Musical.ly to TikTok
Musical.ly was a lip-sync app that merged into TikTok in 2018. Downloaders from that era kept their names, which is why you still see "musically" in tool names today. The name is also often typed as musicaldown or musically down, and several sites use those spellings, so check the address you are on.
Getting a clean sound
The MP3 you save is the audio of that one video, including any talking on top. For the clean track, tap the spinning record on the TikTok, open the sound page, and convert the first video listed (often marked Original). For commercial songs, the sound page names the artist so you can stream the full track in better quality.