What makes the languages (APL, J, K) impressive is that you can simplify what is sometimes pages of code into a single line of symbols (APL) or standard ASCII characters (J and K).
Keep in mind that these languages are the definition of line noise to most coders as having prior knowledge of things like C, Python...etc will do you zero good as the building blocks are completely different from a high level. They might have if-statements in the language, but they're hardly idiomatic. J emphasizes tacit programming which is kind of like a data flow model made up of function application. The languages are quite mathy in some ways, but still approachable.
I find them to be lots of fun, very interactive, thought provoking, and pretty cool. I've only written a little APL & J, but enjoyed how I built my command up from a few built-in primitives.
A problem to me involves reading other people's code which uses primitives I haven't learned yet, or common idioms (Ex: you can make your own average function with a few characters avg=.+/%# so no need to add it to the stdlib). The average function on the tryapl.org site looked a little funny to me...then I realized it worked for not only lists, but multi-dimemsional data structures of n dimensions like tables or lists of tables. I imagine it takes awhile to become proficient.
Surprisingly, both J and APL have some decent support for things such as graphics, but they are still small communities compared to languages we know and love like Python.
In short, give it a try. J has some built in documentation called "J labs" that is submitted by the community. Dyalog APL has a free version for non commercial use and the excellent tryapl.org. Try not to be turned off by the bizzare symbols in APL. They have a long history and are easy to enter with either the IDE or keyboard (especially if you buy one from Dyalog with the symbols on the keys). The inventor of APL got the Turing Award awhile back (later invented J). It was also a big IBM product back in the day and is still used by companies like Volvo.