To build kernels and compile applications for the Explora you'll need a cross compile tool chain. This assumes you're working on an X86 based PC running Redhat linux 7.x. I use the Montavista Software Journeyman tool chain, which was freely distributed at one point. It's a little dated now but it's still quite valid.
You can build your own tool chain from scratch, but that's a lot more complex.
1. At a minimum, get these rpm's via http