The Red Big Builder 3D printer has both front and rear extruders.
Please review the operating instructions to familiarize yourself with this amazing and fragile 3D printer.
Please keep filament loaded in both front and rear at all times during the print cycle. Remember to "autohome" and check the bed level before each print. There is a working profile in the Cura slicing program on the 3D printing computer. The instructions are located in the bottom of the build area of the printer for easy reference.
If you are not familiar with Cura, you can access a quick tutorial at: https://3dp.com/cura-tutorial-3d-printing/