I dont know if this is the right subreddit but why is kanji pronunciation so confusing and hard to remember and how do i make more sense of it?

https://preview.redd.it/l9uuylys16hf1.png?width=1366&format=png&auto=webp&s=9d90753860e970c92d2cf820dd73518a15904042

Im a beginner in Japanese and im trying to learn kanji, this is a screenshot from anki flashcards, I was really confused with all the pronunciations. I saw this and knew it meant 20 days, but I thought the pronunciation would be "futa-jyuu-ka" or something like that. How come it was "ha-tsu-ka" instead? and why is there so much pronunciations for each kanji?

PS, the other programs I'm using to learn Japanese are Bussu and Renshuu. Are those good choices?