In the page you link to, there are two different programs, so two different images.
If you want to separate them in the same sketch, add an offset to all y coordinates of the second program.

I am new to javascript and new to drawing and trying to learn drawing. Please tell me how I can add an offset to y coordinates ?
Thanks

Not sure if this is what you want but try it

1. size(100,200);
2. 
   
3. noFill();
4. stroke(255, 102, 0);
5. line(85, 20, 10, 10);
6. line(90, 90, 15, 80);
7. stroke(0, 0, 0);
8. bezier(85, 20, 10, 10, 90, 90, 15, 80);
9. 
   
10. translate(0,100);
11. 
    
12. noFill();
13. stroke(255, 102, 0);
14. line(30, 20, 80, 5);
15. line(80, 75, 30, 75);
16. stroke(0, 0, 0);
17. bezier(30, 20,  80, 5,  80, 75,  30, 75);

" I am new to javascript"
Well, Processing is primarily in Java...  You can run it in JS, but by default, in the PDE, it is Java.

" how I can add an offset to y coordinates ?"
With the code as shown, you have to do it by hand, with mental calculation or with a calculator...