Sing is a simple language (simplicity is a value !!). The sing Quick Tour makes of you a Sing expert in less than an hour.
In the Reference guide you can find the few information you missed in the quick tour and that fully define Sing.
Built-in functions is the reference of all the embedded polymorphic functions.
If you want to use Sing in an existing C++ project take a look at Interfacing Sing and C++
In the F.A.Q. page you find some explanations about the choices behind the Sing architecture and a couple of work arounds.