Ya, you'll probably want to learn a efficient text editor. People pretty much use whatever they want. There are literally hundreds of text editors. GUI ones, ones inside of IDE's, terminal-based editors. The majority of people though will use either the gui or the text versions of Emacs or a Vi clone (Vim (although that isn't so much a clone), nvi, and such). But by no means restrict yourself to those if you don't like them. Some people are quite happy with something like nano.
Vi is a old fasioned text editor. It uses a 'dual mode' sort of operation were you have a command mode and then a editing mode. You start off in command mode were you can use keyboard combos to manupalate text. Vim is commonly used in Linux distros and it's "Vi IMproved". It sports advanced features like ctags, regular expressions, numerious language extensions, even some introspection. You can set it up to turn tabs into "4 spaces" or "8 spaces" or "real tabs" and then get into flamewars about which is the one true unix way. That sort of thing.
To some people it is the pinnacle of efficientcy. Fast, effective, and a result of decades of evolutionary software design. Other people feel differently. I've heard it described (I am paraphrasing), "A obsolete throwback from the 70's with a interface designed by spastic alien monkeys"
But the principal advantage of Vi is that it's ubiquious. Everybody has one. Every system you use. Every Linux distro, ever BSD fork, every unix system you come across anywere at any time will more then likely have a vi clone aviable. It's a standard feature.
Then there is Emacs. Emacs is something else.
Emacs is best described as:
A. Writting in Lisp (it's it's own programming environment)
B. Not Vi.
And that's about it. There is a old joke that goes along the lines as:
Person A and Person B....
Person A: Oh god vi sucks.
Person B: You should use Emacs
Person A: No thanks, I already have a operating system.
With extensions you can use it to edit text. You can use it to edit text with vi bindings. You can use it to rip DVDs, or browse the itnernet. I've seen extensions were you can manage your mp3 collections and get little previews of albums from gifs downloaded automaticly from Amazon. And you can also use it to program.
When you mention "kernel" and such you make people think that your most interested in low-level operating system aspects. Drivers, kernels, library files, and stuff like that. Stuff that is fast and classic. It's all dominated by C and GNU utilities.
Otherwise if your interested in just application programming.. Pretty much any language you prefer can be used although what you use will probably be dictated by your environment your targetting. But anything will work.. Perl, Python, C#, Objective C, C, C++, Ruby, etc etc.
There are some IDE's.. Eclipse is beleived by it's uses to be 'Enterprise' while Microsoft Visual Studio is what small timers use (they are a bit delusional, well more then a bit.). There is Kdevelope which is KDE's development IDE. They use C++ mostly. And lots of other stuff beyond that.
Just pick something your interested in and begin looking at the code and playing around with the tools. There are also many many numerious unix/Linux programming books.
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