Hey man, I don’t have too much experience in later years with these online beat selling stores, but the formats haven’t changed in years.
.WAV is your high quality file (which artists will use to record.)
.MP3 is your lower quality file, still acceptable for listening, but not for working with on a professional level.
Trackouts, also known as stems, are when you render each sound to its own file for the whole length of the song.
This gives the mixing engineer full control over the whole song, but they don’t have access to your .FLP (FL Studio Project.)
In order to create these trackouts/stems, you have to make sure that each individual sound is on their own mixer insert.
On the actual export window inside FL Studio, you’ll see Split mixer tracks. That will render each sound into its own file.
These trackouts are usually around 2GB for the whole project, to give you an idea.