I think this blog post may clarify things a bit, and give you some new ideas in terms of ways of using the Fluent Forever methodology: https://fluent-forever.com/italki-tutor-guide/

The short answer to your question is that you're definitely right,  you need to know how to say certain sentences in French for example, like; "I want to go to the movies" and "Do you want to go to the movies?".  Somehow you need to get that information, whether it's from a grammar book, a website, a class or a tutor on iTalki.

Once you know that information, you need a way to remember it. That's the purpose of the flashcards at the end of the book.

If you're asking something like:

"Voulez-vous aller au cinéma?" (Would you like to go to the movies?)

The words, in order, are:

[You want] - [you] [go] [to the (masculine)] [movietheater]

You may have a bunch of new words to learn, and some of the word order things here may be surprising and worth memorizing. The way  "vouloir" (to want) changes into "voulez" (you want) and "à le" (to the) contracts into "au" - all of this is new and valuable, and hard to remember.
You can use word order, word form and new word flashcards to get all of that to stick in your head. You'll see a lot of examples in the iTalki tutor guide I linked above. It'll also give you an option for the first half - how do you figure out ways to say "I want to go to the movies" or "Do you want to go to the movies?"

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