A stack and a queue both hold items, but they express different kinds of work.
Choose a stack when the newest unfinished item should be handled first. Think undo history, nested brackets, backtracking, or depth-first traversal.
Choose a queue when items should be handled in arrival order. Think task processing, customer lines, event streams, or breadth-first traversal.
The deciding question is simple: should the next item be the most recent one or the oldest waiting one?
Find more data-structure guidance in How to Choose the Right Data Structure.
