"What is it ?"
If you complete the Duo lessons, read the comments, follow the links there and make some effort to practice listening to French, you will absolutely kill any French course you take. Well, maybe if you're going into third or fourth year university level it will take a little work.
If you want a vocabulary builder try Introductory French at Memrise. They simply present you with a seemingly random collection of French words with a number of attached mnemonic helpers. This is followed by a quiz. They use an algorithm to remind you when to review previous exercises, in keeping with contemporary theories about the ideal time to reinforce recently learned material.
I have learned a couple of hundred words so far complete with accents and elisions, gender etc. The course that I am using doesn't use phrases or such so there is absolutely no grammar introduced or even possible.