STEP 2: Search the web for the lyrics of your desired song (you either have to find a ".lrc" file or lyrics with timestamps for example "[00:04:02] Some lyrics text"). If you find a lyrics file that's great or find lyrics with timestamps you have to create a ".lrc" file.
STEP 3: Now you have to rename the file you created in this way: <song_name> - <artist_name>.lrc or for better matching copy the <song_name> and the <artist_name> from the tag editor and then rename the file.
STEP 4: You have to copy or move the file into a location on the SD Card: whatever_sdcard/RetroMusic/lyrics/ and paste inside your ".lrc" file in there.
A: Retro Music uses the native media player that comes with your Android phone, so as long as a file type is supported by your phone, it's supported by Retro Music.