Anki is what's called “Spaced Repetition Software”.
“Spaced repetition” is a way of learning which spaces ideas over time. For example:
if I were to tell you that my phone number is 07700 900796, you would repeat it to yourself a lot, until you needed to use it again.
If I asked you tomorrow, you would forget it.
If I asked you in 5 minutes, you might remember it, then if I asked you in an hour, you might remember it, and if I asked you this evening, you might remember it.
For a complex piece of abstract (weird) information like a mobile phone number, I might have to ask you a lot; the “spaces” would be quite small so as to ensure you would remember it.
To try a more useful example:
What is the capital of Luxembourg? Luxembourg City.
This is a piece of information where there is a contextual clue. Luxembourg is a tiny country so it makes sense that the answer would be Luxembourg City.
If I asked you this question in 30 years, you might forget (assuming you didn't read about it in the mean time). If I asked you in 10 years, you might have forgotten. However, if I asked you in 5 minutes, you would probably remember. There is therefore a time between 5 minutes and 10 years where you forget the capital of Luxembourg.
Anki (the Spaced Repetition Software) is designed to find this point, and ask you the question when you need to be asked it so you don't forget it.
In reality, the “spaces” will change for each bit of information, simple bits of information can be given bigger gaps (which you're able to customise on Anki) and more complex bits will need to be given smaller gaps (again, customisable).
This is what I've been doing for the past few months: learning, a lot.
It doesn't help you “understand” much, rather it means a lot of facts are swimming around in your head, but this helps you understand. I know the Boxer Rebellion was 1899-1901, and I know the October Revolution was in 1917. Knowing these two facts helps me map out revolutionary history in my head, making it easier to fill in the gaps with more reading and general knowledge.
Professional quizzers talk about hanging pegs. Knowing one thing, helps you “hang” another thing onto it.
Given I know Oscar Wilde's De Profundis was released posthumously in 1905, helps me because I can imagine him in Russia, for the First Russian Revolution as a ghost, just watching. This visualisation means I actually half the number of things I need to remember, and my brain makes the rest of the jumps itself, without me having to force myself.
Anki is helping me to grow my snowball of knowledge, and I love it.