We assume that you have gotten a working compiler set up. The compiler you need depends entirely on the platform you wish to use KOS with. At the moment, only the DC platform is very well supported. The others may or may not compile at this time. So this document will focus on that aspect of KOS.
The first thing you'll want to do is get a working binary image of the KOS libraries. You may download KOS in binary or source form.
If you downloaded KOS in binary form, then you'll still need a binary for genromfs if you want to use the ROMFS file system (which will probably come in quite handy for development). Linux tends to come with this binary, BSD users can compile one using the copy included with the KOS sources, and Cygwin users will likewise need to compile it or obtain a binary from the same place you got the KOS package.
The first thing you'll want to do in either case is to customize an ``environ'' script. This script is run inside your shell to set various environment variables so that the KOS build scripts and tools know where to find KOS and the compiler toolchains (for DC, an SH-4 compiler, and optionally, an ARM7 compiler). Look in the doc tree for samples. If you are using bash (the default for Cygwin) then you should start with one ending in ``.sh'' and if you are using tcsh then you should start with one ending in ``.tcsh''. Generally it shouldn't take more than changing a few base directory variables at the top of the file, and the environ script will be ready to go. You then need to either execute this script before working (``source environ.sh'' or ``source environ.tcsh''), or put the appropriate command in your shell's startup script. The instructions on how to do basic shell things like that is beyond the scope of this document, so look to Cygwin and/or *nix help groups if you want to find it.
Now that you think you've got your environ script setup correctly, type set (under bash) or setenv (under tcsh) and look at the environment variables. You should see a whole bunch of them starting with ``KOS''. If that's true then this step is probably complete.
If you downloaded the source package for KOS, then you'll want to compile it now. Just change the directory to the root of the KOS tree (e.g., inside ``kos- 1.1.8 '') and type make. After a few minutes everything should have completed successfully. If not, then you might need to recheck the above steps and make sure everything is set up properly. If all else fails, try asking on the dcdev or cadcdev-kallistios mailing lists.
Well, now that that is (hopefully) out of the way, we'll proceed on to writing a KallistiOS program.