Mod is a tool for creating a new Fuchsia mod project scaffold. To use it, first include the tools/bin directory to your path.
export PATH=${FUCHSIA_DIR}/topaz/tools/bin:${PATH}
To create a new mod project under the current directory:
mod create <your_project_name>
This will create a new mod project with the given name in the current directory. Note that it doesn't automatically add the project into the GN build tree (yet). You should manually add a new package definition somewhere in your BUILD.gn files order to see the new mod on the target device.
Run mod help for more information about the detailed tool usage.