Please, keep in mind that this tutorial designed for Marlin / Repetier firmwares, it is not guaranteed to work with another firmware,
What is a 3D Printer G-CODES?
G-code (a.k.a RS-274), which has many variants, is the common name for the most widely used numerical control (NC) programming language. It is used mainly in computer-aided manufacturing to control automated machine tools (like CNC’s and 3D printers). G-code is sometimes called G programming language
How to send 3D Printer G-CODES to the printer?
In repetier host, you should first connect the printer, then go to Manual control and write the code on this box:
then just press SEND.
In Simplify3D, you need to open the tools > Machine control Panel. in the control panel, choose Communication
Remember!, the letters should be in in CAPITAL, example: G1 X-1 Works | g1 x-1 may not work