Guide

Install Anki
Download the deck: the blue "Download" button is located at the end of the description, right after the "Sample (from X notes)" section.
Remember to enable the Don’t play audio automatically setting from the deck's options.
Consult the Anki Manual if you have other issues or questions regarding Anki.

The hard fact is that Anki alone won't make you fluent in Japanese (or any language).
That's why immersion needs to be the top priority. It actually teaches you how to use the language in the wild, so prioritize it above everything else.
Anki decks should only play a supporting role, boosting your vocabulary, grammar and kanji and making all that immersion and overall experience a lot smoother and enjoyable.

Learn the normal Hiragana and Katakana.
Get the gist of the extended kana. There is no need to memorize them, just get used to how kana sounds combined with other kana.

Go through each JLPT N5-N1 subdeck (vocab and kanji) one by one.
It can be considered a "core deck" as well, as it contains common/essential words and kanji used in everyday Japanese (both in real life and in anime/manga).
Important note: The JLPT entries are based on words and kanji from past exam papers (up to 2011). This subdeck alone will not guarantee exam success and should be used alongside active learning, immersion and proper study methods!

Use all the "reference material" subdecks for a quick search when you need to look up radicals, kana, kanji etc.
As for the "ready-made mining material" subdecks, all cards are suspended by default (if they are not, suspend them). Over time, unsuspend and learn the ones you find useful.