Memory has been shown to be fundamental to our thinking and understanding. It is impossible and pointless to remember everything we learn or discover. But there is some information that we clearly see the value in remembering. Our brain does move some information from short-term memory to long-term memory based on repeated use in the near past. However, not everything we want to is placed in long-term memory. I recently read Michael Nielsen's essay on augmenting long-term memory, that described the concept of spaced repetition and the use of Anki as a tool to achieve this. I highly recommend reading this essay if this topic sounds interesting to you.
I had used Anki a few times in the past. I was confused by its concepts, UI and usage and did not get any benefit from it. After reading Nielsen's essay, I started to actively use Anki again and this time I am seeing some benefits. This is a very short guide to using Anki based on solely on my usage.
At its simplest, Anki allows you to create flashcards and practice revising the cards. In Anki, flashcards are organized into decks. A flashcard has to belong to exactly one deck. You can create as many decks and flashcards as you wish.
Flashcards are used to test and improve memory. When you create a flashcard, you provide a question and its answer. When you are tested, you are shown the question of the flashcard and the answer is not shown. You try to recall or formulate the answer. Then you look at the flashcard's answer and check if you were right or not.
The advantage of Anki over a paper flashcard is that after answering the card, Anki will ask you how easy or hard it was to answer the card. It provides up to 4 options for you to pick: repeat, hard, good and easy. If it was easy, then it means that there is no need to test you on that card for a long time. If it was hard, then it means that you need to be tested on that card soon in order to help your recall of that. Anki takes care of maintaining the statistics for every card.
Keep a single deck: You can create multiple decks, organized by topics. For example, initially I created multiple decks: world history, economics, English, algorithms and so on. After trying this for a while, I have now come to agree with Nielsen's recommendation that it is best to just keep a single deck. This makes adding new flashcards easy. And it makes your revision very easy. As with any activity, the easier it is, the higher the chance you will do it regularly. Also, by being tested on questions from any corner of human knowledge, you sometimes start to see the connections that lie between them.
Revise once a day: You can revise your deck at any frequency you want. You do this by clicking on the deck you want to revise. Anki will start showing you the cards that it thinks you should revise today. You can stop the revision at any point and return to it at any time. It does not matter. Anki is very convenient! I tried wildly varying revision schedules and have found Nielsen's recommendation of once a day to be the best. Anki too is designed for revising once a day, so this works best. If you do it regularly, you will find that revision takes 5-10 minutes. If you skip revision for a day or more, you will see that the number of cards to revise has increased.
I have found it best to use the Anki app on Android for revision. My phone is on me at all times, so I can quickly revise a few questions while I'm using Uber or waiting in line at lunch. During revision, I sometimes find that I want to correct or improve a question or answer. These actions can be done using the Android app.
I have found the Windows and Linux apps to be best for adding cards. I mostly read technical blogposts, research papers, longread articles and essays at my computer and it is these tasks that usually lead me to add new flashcards.
I have an account on AnkiWeb and use that account on both the Android app and Windows/Linux apps to keep my flashcards synced. Anki will also remember your revision statistics. So, you can revise on the Windows/Linux app one day and revise on the Android app the next day and on AnkiWeb the next day. This whole service is so convenient!
I have found it best to make the question and answer of a flashcard to be as small and atomic as possible. If your information is not atomic, then break it down into multiple flashcards until each one is atomic.
Other than plain text, you can also add formatting and images to your flashcard answer. There are plugins to the Windows/Linux apps that allow you easily add formatted source code and so on. I have found it best to restrict myself to plain text and images.
Do not restrict Anki just for study or research. Use it for everything and you will find it to be truly useful. Here are some examples: recalling the name of a particular tree you see, recalling the word that has a specific meaning, recalling a phone number that you always forget, and so on.
Writing a good flashcard that works well for you is an art. You will see yourself improving in this aspect as you use Anki more. For example, I wanted to remember a math function that is common in deep learning. Initially I had added "Q: What is foobar? A: It is this math formula." After revising that card a few times, I realized that what I actually wanted was a mental picture of the graph of that function. So, I edited that card to "Q: Recall the graph of the foobar function" and I replaced the answer with an image of that graph.
I have not found much value in taking cards or decks shared by other people online. Using shared decks might be useful if you are preparing exams like GRE or a medical exam. But since I am using Anki generally for my memory, I have no use for shared decks. What information I tend to forget, what I would value to remember, what form I would like to have it in is very personal. Also, writing down my own flashcard feels like a useful mental exercise.
To summarize: make your flashcards atomic, keep a single deck, revise once a day, use phone app to revise, desktop app to create cards and AnkiWeb to sync the cards.