Testnet instructions are here: http://doc.tzalpha.net/introduction/alphanet.html
Best I can tell: smart contracts like Ethereum, except the protocol has means for amending the protocol itself? So, meta-Ethereum?
This article (Linda Xie) is pretty good: https://medium.com/@linda.xie/a-beginners-guide-to-tezos-c96...
Apparently they also already have proof of stake?