What other types of "interaction" are there in the tech-field?

I apologize, but how exactly do they share the same index? I'm a bit confused here.

What situations do programmers have direct control over how data flows between these 3 components of a computer?

if new leaf nodes are never created then how are new nodes put inside the tree?

At what point (or number of element) does the code shown above start struggling and becoming inefficient?

I think it's nice how the array list is able to expand and change over time instead of having a set amount of spaces (like the int array). Is there a simple command to add a number to the beginning of the list instead of the end of the list?