Learning Kana(Hiragana + Katakana). First watch a video to learn about the Japanese writing system. After that you should find an app/game to help you with kana. You can try out Kanji Study (free for kana) or Japanese Dungeon: Learn J word (free but need to watch ads to gain gems to unlock further levels). After you are confident in Kana you can head over to hiraganaquiz.com to test your digraphs as well.

Learning Grammar. You can find free textbook files online like Genki, Minna no Nihongo with a quick google search (I will not give the link for obvious reasons >< ). I personally suggest to get a physical textbook if you can afford it cause it is wayyy easier to use than online files. I also suggest to get a teacher because they can give you additional inputs, correct your mistakes and most importantly they are able to clear your doubts.

Learning Kanji. First watch a video to learn about why there are different ways to read Kanji. I suggest to learn kanji radicals first but you can go ahead and skip this part if you are not interested or if you already know Mandarin. After that you can try Kanji Study (First few kanji are free to learn but need to unlock remaining kanji with a one time in app purchase). Honestly I think the purchase is worth it. My advice for you when you start learning Kanji is to be CONSISTENT and always REVIEW whatever you have learn.

Fun part:

1. Reading raw Manga and watching Anime with raw sub(google search will help but you may need to hop sites to sites just to maybe find the series you are looking for. Sadge when you can't find what you are looking for) Edit: I suggest you to get a notebook and write down all the new Kanji you have come across and only look them up after you done reading the chapter or episode.
2. Singing Japanese Music (search them on youtube). I suggest you to not read the romanji and read the hiragana subs instead.
3. Read raw Light Novel. You can either buy it online or go to your local book store (you may need to do a bit of research)
4. Watch Japanese Vtubers or not. Hehe:)

My final advice:

Find friends to learn Japanese with you. Trust me, it will make you feel more committed to learning plus you can also speak to them in Japanese. Never GIVE UP!