Look here for introductory and platform stuff.

Technical Online Help | (sageerpx3.com)

Let’s build great things together | Sage Developer

https://online-help.sageerpx3.com/erp/12/technical-online-help/

courses and more documentation is availabe from Sage University.

Many thanks. I checked all these resources few days ago and I noticed that there is a shortage in 4GL documentation (syntax ...). 

Any way, I highly appreciate your help

Hello Noussayba! I'm an X3 developer and in your new journey, one of the links that will help you the most will be this one:

https://online-help.sageerpx3.com/erp/9/wp-static-content/static-pages/en_US/v7dev/index.html 

Many thanks, I highly appreciate it

Many thanks, I highly appreciate it 

Hi Zivanai B,

Thanks, for sharing it. 

Best Regards,

Daniel

Try these:

- Keywords: https://online-help.sageerpx3.com/erp/12/staticpost/x3-script-keywords-glossary/

- Main development platform: https://online-help.sageerpx3.com/erp/12/wp-static-content/static-pages/en_US/V7DEV/getting-started_home.html

- Depending on your situation, you may need to delve deeper into adonix (original X3's company before being taken by Sage) Windows documentation (external hosting link by lvexpertisex3): https://lvexpertisex3.com/x3help/ENG/MODEL/APRES_MOD.htm

-- If you took Sage University, then this should be covered by the designated X3 Development instructor.

Other than that, like Stephen said, Sage University. Especially if expected to create from scratch.