That's an excellent question; one to which I would also like to know (more) about. So far I've thrown a bunch of money at it to just buy random pieces and cobble them together in spare time and see what happens.

So I have raspberry pis; I have arduinos. I've done some simple programming for both, to read from sensors. Water sensors and thermal sensors and buttons and sound pins all on breadboards were fun.

I figured I was ready for the next step: soldering together a kit. So I soldered together an ethernet kit for the arduino. That project fell flat: the arduino powered up while the ethernet shield did not; the arduino reported that it didn't even "find" the ethernet controller even though it was piggy-backed onto it. Usually when you plug in the RJ45 jack to a NIC you at least get the lights on the RJ45 port to light up. But no dice for me here either. And I have no idea how to debug that problem.