Cairo Language Server
Scarb is distributed with the
scarb cairo-language-server extension which is a compilation of the official Cairo 1.0 Language Server, that is matching the version of Cairo compiler used in Scarb itself. Scarb's version of the language server is just a launcher for the original code, unmodified.
Visual Studio Code
The Cairo 1.0 Visual Studio Code extension will start language server from Scarb automatically. You do not need to take any further steps. Consult extension's documentation for more detailed information.