The sound, as TikTok stores it
Every TikTok has a sound: the creator's own audio, or a song picked from TikTok's library. TikTok keeps that sound as an MP3 file of its own, and that file is what PocketTok downloads. Nothing is converted on the way.
Because it's the sound rather than the video's soundtrack, a video that talks over a song gives you the song on its own. For a video in the creator's own voice, the sound is that voice.
Videos and slideshows
Photo slideshows have a sound too. Paste the slideshow's link and Download MP3 sits next to Download all; the photos themselves are on the TikTok slideshow downloader page. For the video with its sound, use TikTok to MP4.
Use it fairly
Songs belong to their artists and labels, and original sounds to the people who made them. Download sounds for your own listening or for content you have the right to make, and credit the creator when you use their sound.