As of Proof of Concept 4 (POC4), smart contracts are written in higher-level languages such as Serpent (Python inspired), Mutan (Go inspired) or LLL (LISP inspired).
Whichever high-level language you opted to write your contracts in, this code is compiled down to EVM-code, the machine-readable code that runs on a virtual machine built in the Ethereum clients.
Tutorials are few and far between, and mostly written by the community: this is by design as we are rapidly iterating over each Proof of Concept and their feature set is changing quickly. We will of course issue extensive documentation for all reference clients, our APIs, etc, as development continues.
EVM-code, previously refered to as "EtherScript", will continue to improve as we develop the language. Right now we are at version 1, but Vitalik has released information about the upcoming version 2. This does not impact your Serpent, Mutan or LLL code: compilers will take care of converting to the 'current' version of EVM-code.