Knowing C language.
https://github.com/Stephane-D/SGDK
https://github.com/Stephane-D/SGDK/wiki
In the IDE of your choice (i use Visual Studio Code), type the following command in the terminal :
[sgdk_install_folder]\bin\make -f [sgdk_install_folder]\makefile.gen clean
Then :
[sgdk_install_folder]\bin\make -f [sgdk_install_folder]\makefile.gen
where [sgdk_install_folder] is your SGDK install folder.
If your SGDK folder is "C:\sgdk", then the commands are :
C:\sgdk\bin\make -f C:\sgdk\makefile.gen clean
and :
C:\sgdk\bin\make -f C:\sgdk\makefile.gen
The compiled rom will be in the "out" folder.
Enjoy !