Everything, except of modififying files as to be done within a chroot environment. Execute the newly created alias cr to change into the build system.
Now you can go into the folder build/ and just execute the command make to get an overview which parameters are available. A more detailed explanation will follow later.
The first command you should execute is make unpack, after that you configure the build system via the command make menuconfig.
Now you can start the build process: make build install iso dist
Once this is done, you find in the directory build/dist a ready to use DL version. ;-)
When you're working on DL and want to test the ISO with e.g. VMWare, then you can skip the make dist part and you find a useable ISO image here: build/tmp/bootcd.iso
You can create a configuration floppy disc by invocing the command build/scripts/build-etc
Do not execute any make command outside the chroot environment! Otherwise you will have to re-install your host Operating System.