This teacup subcommand configures Tcl installations to use teacup's local store for packages. ActiveTcl comes already preconfigured to use teacup's local store.
How this works (in 2014) is by installing necessary packages and modifying init.tcl to auto-load the activestate::teapot::link package, which in turn extends auto_path to include the teapot repository specified in info library/teapot-link.txt.