It transports the (horizontal) rocket to the pad, erects it, and provides umbilical connections for power and fuel to the rocket during launch; TEL.

You can see them disconnect in the video I linked.

SpaceX does similar; https://en.wikipedia.org/wiki/Transporter_erector / https://en.wikipedia.org/wiki/Transporter_erector_launcher

> SpaceX uses the central spine of the transporter erector as a strongback, restraining the rocket, providing stability until the tanks are pressurized with fuels, and contain the fluid hoses along with power and telemetry cables. Consequently, it remains at the launch pad through the launch and is typically tilted away 1.5° from the rocket just a few minutes prior to launch and 45° away from the rocket at the moment of liftoff.

The Shuttle's https://en.wikipedia.org/wiki/Mobile_launcher_platform played a similar dual role.