Answer 1

see....
suppose u have an array of 5 space...
4 are filled..
now any 4 can be filled and u can add a value to the remaining void array index...

but array push()
means...its a stack
same as stack / pile of books..

u need to add(if u want) to the top...
suppose a book self is there..
filled left to right with remaining 2 positions for 2 books..
so its like u can push 2 books...to that postion...

for stack-queue implementation we code the push function...its a idea...
it works as code is written..
for stake or queue...
only upper position u can add values or datas...
((up to end of array length))

....... position 6
....... position 5
--- position 4
--- position 3
--- position 2
--- position 1
--- position 0
suppose this is a stack..
u can first push a data/element/value to the 5 th position then 6 th position..
and then stack is full