Is the documentation you provided also in C?
The first link, yes. Second link, no.
I think that the C docs, in particular the introductory sections, are probably worth looking at because they were written by actual human technical writers before Apple fired them all. The modern docs are automatically generated from the code and much harder to understand, especially in terms of understanding the basic concepts. But if you get totally bogged down by not understanding the C, then just use the Swift docs at the second link.
is there a way to include a C file in a SwiftUI project?
Yes, but you probably don't need to do that.
What are values, keys, and dictionaries?
In Swift:
https://developer.apple.com/documentation/swift/dictionary
In the C code you're looking at, it's doing essentially the same thing but in a much more verbose fashion because these things are not built in to the language, but requite lots of library function calls to use.