The easiest way to build your own firmware without needing to create your own keymap compiling environment is to use either QMK configurator or the real-time keymap editor in the VIA app. In order to use via you need to download the correct firmware for your PCB (The file name is typically just the name of the PCB) from VIA’s website. Then flash that to the PCB. To use QMK configurator you will need to go to the QMK config website and load the correct keymap for your PCB in the “KEYBOARD” box. Next, give your keymap a name in the “KEYMAP NAME” box. Now you can start to build your layout. To do this all you need to do is select the key and the keystroke you want it to register. You can edit various layers to give you as versatile a keymap as you need. Once the layout is done, click the “COMPILE” button and wait for the process to complete. After compiling you can click the “FIRMWARE download button” and your .hex will download ready to be flashed.