Hey Abbasi!
I think the best way to learn about security is doing the Become Rapid Developer learning path.
There you have a part that explains how the security works on mendix. You can check it on this link:
https://academy.mendix.com/link/modules/96/lectures/787/9.1-Introduction
Kind regards,
Emilio
Indeed excellent suggestion by Emilio. Next to that you can check out the documentation.
I would also suggest filtering on "Security" on the Learning Paths page in Mendix Academy.