With the Basic program you get access to all our videos and audios, but not Quiz mode. You can access the "Watch" section, which includes our interactive subtitles, but not the "Quiz" section of each video. You do however, get access to Ready for Review, which includes exercises to help you retain the vocab you learned from the videos.
With the Plus plan you get access to Quiz mode, which includes personalized quizzes and other exercises to help you learn. Also, you get personalized flashcards, and the ability to download Learn mode and the audios if you want to study offline. You also get printable PDF transcripts of all the videos.
So, with Basic you get all our videos and their subtitles, the My Vocab sections and the Ready for Review section. With the Plus plan you get that, plus all the other perks listed above.
But the best way to find out is to jump in and give FluentU a try!