French is nicer phonetically than English in that if you see a word written, you automatically know how to speak it given a few rules. The reverse is not true - hearing a word does not tell you how to spell it (notably because a lot of letters are silent) but that's not a problem for learning French this way.
Your first task is to learn the rules of how to pronounce a word that you see written. Unfortunately this app does not have that capability yet, so just use YouTube, Google, or ChatGPT. Don't worry about being 100% capable at this - you'll be able to check your pronunciation as you use the app to memorize words anyway, so you just need a foundation to start with.
Remember: vowels are very important in French, practice saying the vowels out loud and see if you can match the audio in whatever tutorial you use. Don't worry too much about the 'R' consonant sound, it doesn't matter for comprehension. You wouldn't believe me if I told you how sensitive French speakers are to the subtle differences in vowels, and how forgiving they are with consonants.
Using this app is just testing yourself on flashcards with an English prompt and a French answer (or multiple answers).
A flashcard is represented as a little green square that's inside a bucket (dotted lined rectangle) or falling between them. You click on a bucket, and then it randomly selects a flashcard to test you on.
The flashcard will prompt you with something in English and you see if you can recall the same thing in French by clicking on the card. Obviously the first time you see the flashcard you will fail because you haven't seen the answer yet. It's up to you to select Pass or Fail. The best way to test yourself is to say the answer out loud (or at least speak it internally in your head if you're in a crowded place and too embarassed to say it out loud) before revealing the answer.
BE HARD ON YOURSELF. There is only a small penalty for failing - if you fail a card that almost made it to the end and you ALMOST have it memorized, it won't be a big impact on your studying progress to fail it back to the top. The reason is that to send a flashcard that you know very well (and can recall quickly) through the entire cascade takes very little of your time and effort. So don't be afraid of failing a card just because it's close to the finish line. Take pride in being super strict on yourself and failing answers that are just slightly off.
I repeat: BE HARD ON YOURSELF. Definitely fail yourself if you get the gender wrong. Definitely fail yourself if you say a different vowel than the one it's supposed to sound like.
Remember that pronounciation is very important. So to make best use of this app, after the reveal, you should click the little speaker icon on each answer to see if the way you said it sounds like the way it's supposed to be said. If not, fail yourself. Eventually you'll be confident enough in your ability to pronounce any given word that you can stop clicking the speaker icon.
You start with many (hundreds of) flashcards in the top bucket, called "start". Don't test yourself on all those hundreds of cards before working your way through the cascade, just start with a few. Each day try to bring a few more cards into the cascade from the start bucket, but do that at the end - most of your daily study should be trying to get the cards already in the cascade down to the bottom.
The best way to use this app (and memorizing things in general) is to do it every day. A memorized word or phrase is reinforced in your brain whenever you correctly recall it. If you forget to use the app for a week, you'll simply find that you've forgotten the cards near the top of the cascade, and lost an opportunity to correctly recall the card after sleeping on it for a night (and therefore to get one more pass of reinforcement). But that's no big deal, it's just a minor setback.
I don't know how many cards you need to study to be fluent, but I've noticed that every time I increment by some hundred or couple hundred I notice a significant improvement in my daily life in France. Once you get to one or two thousand you'll be able to do quite a lot in French.