Is there a mini-tutorial or a list with a short description for each filter provided by Nik Software?
If you go to their site, click on a product, such as Color Efex Pro, then you'll see "Filter Samples" with an image sample and description for each filter.
There are also webinars and online tutorials
Nik also has 30-day demo/trial versions of their plugins, so you can download and look through them all.
@Bob, although @MikeW is right in saying that you will find a lot of info on-line, in the places he mentioned and on various tutorials on YouTube, working with NIK requires time and a lot of trials -- OR just keep to the basics, but then there's not much point in it.
"Color FX" is my favorite suite for doing all kinds of modifications to pictures. The thing that makes it fantastic, though, is that it's modular. Like an audio processing chain in a studio (if you know nothing about that, think "guitar stompboxes"), you can insert as many FX as you want, each will have many parameters, they will affect each other down the chain and there really is no "Color FX for Dummies".
In other words, yes, I can tell you "detail extraction" will be a bad move for soft portraits, but how can I tell which of the 3 ~ 5 contrast related FX you should use depending on the situation?
Can't write a book here, so I'll leave you with the usual basic advice, "experimentation is key", an encouragement, "it's really worth it, much more so than anything Adobe has been producing lately" and, sorry if it makes life worse, I have to say the Topaz Suite seems to be pretty much complementary.