Each japanese letter has a sound. Learn all the letter and you'll know all the sounds!😁 Start from the simple kana, like か(ka), み(mi), ね(ne). After, learn tenten and maru, that with add more sounds as ga, gui, gue. After, the "little つ, や, ゆ, よ" and the "long sounds".
When you learn all the hiragana, you will can learn the katakana very faster, cause are the same sound just with another way to write. As if you write "a" and "A".
if it's about kanji; learn a word. The word is a word, the kanji is how you write it. So, learn the word and you will know read it, learn the kanji and you will learn write and read that in kanji, but it already will know the word. When you know a lot of kanjis you can guess the read and meanings. As if you read "Someday". You know what "some" and "day" mean, then you can know what them mean together.
I'm sure renshuu has schedules and very better explanations for this😅. Look in "manage schedule> renshuu recomendation> basic japanese> hiragana and katakana" and in "resources> japanese lessons> hiragana and katakana".
It is very hard at first but look up Tofugu online because their learn hiragana page is really helpful - though it’s structured like a massive, massive blog so it may be hard to find - but it’s helping me a LOT with character learning, more than renshuu actually. Plus you don’t need any account or payment or anything. I’m really finding it beneficial for hiragana and I hope it’s the same for katakana! 🤞🏻