I’m incredibly new, so obviously this may be a stupid question, but I’m wondering what the difference between kanji and vocab is in certain instances.
For example, the kanji for “big” is 大, but the vocab for “big” is 大きい. If so, what does it mean that the kanji means “big” when it is merely a part of the vocab (which means the actual word, I guess).
If you read the vocab meaning it explains the difference.
This is the adjective form of big. It has the same meaning, though it is a word for describing. Words that end with い are often adjectives, remember that for future words as well. So, as long as you know the meaning of this kanji, you can transfer that to the meaning of this word. It’s the adjective big / large.
Welcome to WaniKani!
No such thing as stupid questions! Ask away, because it only shows that you want to learn 
A useful way to think about it is that kanji are not words. Kanji are building blocks for words. So for example, 大 by itself is not a word, but a building block. These building blocks have meaning, but do not constitute words in and of themselves.
This is how I try and differentiate it:
Think of Kanji more like concepts. 大 is the concept for big, not the word for big.
Therefore the adjective form for big takes the concept (大) and makes it into an adjective (大きい).
The noun form for size (大きさ) takes the concept for big and makes it into a noun etc.
A system like this (kanji + kana) will apply to many kanji/vocabulary you will come across to mold the concept into an adjective, noun, verb and so on.
This is the simplest and most concise explanation for the phenomenon. I’ll add a little explanation as well. Strictly speaking, from a historical point of view, there isn’t only one meaning for kanji. The meanings that you’ll find in a dictionary today are a compilation of the meanings of the words these kanji make up. Take for example 足. It can mean ‘foot’ when it’s あし, and it can mean ‘to add’ when it’s たす, or ‘to be sufficient’ when it’s たりる. There’s little logical connection between these concepts (there may have been one historically, but who knows), however, since this kanji is used for all these words, all these meanings can be ascribed to the kanji, It’s a rather messy business, but WaniKani usually teaches you only one (max two) of these meanings in kanji lessons, but sometimes you’ll see other meanings in the vocab lessons. Not sure you wanted to know all of this now when you’re just beginning, but it’s something to keep in mind. You can think of the “meaning” part that WaniKani teaches you in the kanji lessons as more of a “keyword” you can associate with that kanji, and use the vocab as an example of the “real meaning”. Same goes for the WaniKani radicals, think of these as keywords rather than the actual meaning of the radicals.
I was just typing a similar response! Well said. To build on that,
Meanings don’t translate directly, they embody their own concept. That is why the definition of a kanji in a dictionary usually has many many english equivalents - there is no inherent connection between english and japanese in the way that our languages connect the universe to words. So while there is a direct translation for obvious concepts and objects like big/ small/ water etc, it becomes much more difficult to translate stuff as you get more abstract. I recommend thinking of kanji as concepts.
For example, 生 means life, natural, genuine, birth, new … etc. We use many words in english to try to get at the meaning of the kanji, but in a japanese mind it embodies a single concept. 生 is 生.
Kanji can be building blocks for other words too.
大学 (DAI - GAKU) could be considered “big learn” but we translate it as College.
大学生 (DAI - GAKU - SEI) could be considered “big learn new/life” or something like that, but we translate it as college student.
Of course, to further confuse you, sometimes a single kanji is a word as well. Like, the kanji 人 (“person”) is a building block of words like 外国人 (“person from a foreign country”) or 人口 (“population”), but it is also the only building block in the word 人 (also just “person”). Or, more confusingly, the abovementioned 生 is a building block in lots words involving being alive, or being a student, but it is also the only building block in the word 生 (“raw” or “fresh”).
So a corollary would be that radicals are the building blocks of the buildings blocks? Sometimes they may coincide and a radical might be a whole kanji unto itself, but other than that they are common components of those same building blocks (kanji) which make up entire words?
Anyways, this is an amazing welcome. This seems like a great community - add it to the incredible user interface of the actual application (as well as my love for Japanese) and this seems like it’s going to be very fun.
Yes. For a sciency analogy, think of radicals like subatomic particles, kanji as atoms and vocabulary words as chemical compounds/molecules.
That’s exactly right.
What a great analogy!
I’ve seen this described in so many ways but never like this. Well done.
Amazing! With the exception of certain kanji which can act as entire vocabs/molecules, then? Or is this something that happens in physics and I Didn’t Even K n o w?
There are some single-atom molecules - like Helium and other gases from its group, that under normal circumstances don’t form any compounds. So that would be equivalent of single-kanji words 
It will be a very Funny Game.
Admittedly, this requires some explanation of how Japanese evolved as a language. So when Japanese started importing Chinese characters/Hanzi to write Japanese, native Japanese words were written solely using those characters. The Japanese word for big is おお, and the chinese character 大 also means big, so the word おおきい is written as 大きい, きい being a suffix to indicate it’s an adjective.
You can consider Kanji a form of pictographic abbreviation, if you will.
This was my default Gravatar pic since I opened my Letterboxd account in 2016 but I better change it soon. WaniKani is wholesome. Funny Games is… not.
