Hi! I'm trying to learn x86 Gnu assembly language from home. And I have a question. Is it possible to draw a rectange on monitor using GAS? How can i accomplish that? I know i have to work at the pixel level but i can't find the correct insturction or syscall to illuminate individual pixel. If anyone can just give me the theory behind it or be kind enough to provide the code I would appreciate very much? Thanks.

There are potentially a few layers between your assembler code and the video hardware. You haven't said anything about what sort of hardware or operating system (if any) you are going to be running your code on. I will hazard a guess that you have already done something similar in a DOS application and now you want to try it with Linux. I am sorry to tell you that you will not have ready access to any low-level resources you may have used in DOS.
Really, to get any sort of reasonable answer, you need to give more detail of the runtime platform to you intend to use.

--- rod.