What do you guys think about this?

First when I saw the page, I thought it was a notes-taking app lol.

Try to come direct to the point in a single line, instead of me looking around and figure out what the product is about. People usually don't have that much time and as others have pointed out, you needn't make the user wait to see what your product is about. It's just wasting time.

Later, try to keep a working demo on your landing page or atleast make an animation / GIF of how the app would work. (If you keep a working demo, it'll be even better because I can just immediately make a flash card and try it out... later I can login once I like it)

Good luck!

I get your choice of not giving a choice to users to suscribe before using your app,
but it's an important choice, because most of the times, I don't go further when I can't test the product right away ;)

Maybe, you should at least get a visual insight of the user experience? (just my opinion).

And regarding the app itself : Interesting concept for the library, but I can't have access to the questions I asked in the library? (Only the first question I created appears on the right. Can't find the other ones).

But can be a cool concept, even though I think it would need to be really more "user friendly", for me to use it frequently

I like the idea & concept. Thumbs up.
What i don't like is waiting for the text content, one at a time shows up. Users in a hurry would just bounce waiting for your content. The Version in the top left corner is a bit unusual? maybe move it to the bottom? I would also add some social proof to your landingpage.
Go on. :-)