I am confused about the differences between know, know about, and know of. Why do they use different prepositions?
Level of knowledge.
I know the C language. I can write programs in it proficiently. I know the caveats and problems.
I know about Python. Basics of syntax, general structure. Given some time and references I might write some simple programs in it, but saying "I know Python" would be too much.
I know of Haskell. There is such a language and it's a functional language. That's about all I know of it.
Even the unqualified verb "know" is weak: depending on your proficiency, use verbs phrases like "am proficient in", "have use on several development projects...". in the field of programming "know" is an vague verb: I know the grammar of C, but have I developed in C?