Not impossible, just a high learning curve imo if you don't have experience or knowledge already in certain things.
And you also need additional programs for sprite editing, sound editing etc.
If you're making a character from scratch instead of an edit, it takes even more time.
I'm saying this as someone who just started learning this myself recently. Its been a slow process for sure but I'm making small steps.
And I don't know what you consider simple, but youtube searches already tend to give me good info on the process of making characters, even from ones like 9 years ago.
For .cns or states, you can just open the basic Kungfu man with Fighter Factory, there's comments made there to describe how and why the values work.
I'd recommend you start experimenting with KungFu man first, since there's guides in the codes. Ready-made characters don't tend to have those.
Also you experiment by copy and pasting states from other characters and into your own and see how they behave.
There's many files sure, but understanding them isn't exactly complicated imo
This is what I've learnt and understood so far, I might be incorrect(if any other experienced char makers wish to correct me, feel free.)
.sff - Your raw sprites.
.air - Animation files, which you arrange your raw sprites in to make animations as well as set hit-boxes(?)
.snd - Your sound files.
.cmd - The file which stores your command inputs.
.cns - The state files, where you how your fighter 'behaves' as a result of your command inputs. Its also where you link the animations and sounds together depending on what state your character is in.
.def - Simple file, but is the one which links all of the above together. Also where you put your character's name, creator's name, version etc.
Its not exactly simple, but...
http://www.elecbyte.com/mugendocs-11b1/tutorial1.html