Hi Aishwarya,
if you want to add a graph to an existing graph indicator you could use the build array function and add all the graphs you want to display into a 2D array. This can be done dynamically to append a new graph every time you click on the button. Two words of caution with this: a) If the arrays you add are too big, you might get memory problems as your program runs and b) for certain functionality it is not the best implementation to pass a 2D array to a multiplot. For some of the crazier stuff you might need it in a cluster, but you probably needn't worry about that now.
Feel free to check back if you have any further questions.
