Official Creality Ender 3 Direct Drive Extruder Kit,
The kit includes the X carriage, extruder, 42-40 stepper motor, and hotend. The whole kit is preassembled.
To install, you remove the original X carriage with hotend, extruder and stepper.
You then put the new carriage on, and reattach all the wires.
This is explained in the included instructions.