So I was wondering how to make a game screen mod in minecraft. Like the Computer from computercraft they can play pong and worm/Snake. And I am wondering how could I make a similar mod?

For a GUI based mod you need to learn about how GUI's work as well as learn how the logic of such games work. In addition to that you should study player input and of course basics of java

 

For a in-world type of screen which renders animation and work as the screens from computercraft you will need to study a lot of stuff. Like how rendering works, how the game code for rendering works and ofcourse knowing some basics of OpenGL doesn't hurt either.

Could I posiblly download computercraft and the open it in eclipse and see how the did it ?

Nope, ComputerCraft is closed source so you can't unless you decompile it somehow and even then it will probably be unreadable to you

 

However you can look at EE3 or Buildcraft's code, since they are open source

Hers the OpenCCScensors addon for ComputerCraft. It's open soruce so you can look at it's code fi you want to see how an addon to computer craft is modded. https://github.com/Cloudhunter/OpenCCSensors

So i just download the src and i can see how its made?

awnser on norwegian please to tired off writing english now

yes you may download the source for that addon mod and see how it's made and no I will keep my language to one everyone can understand so others too can follow this topic and to prevent it from derailing