Key point
One idea
A heap is for priority. Use it when the problem repeatedly asks for the smallest, largest, earliest, or highest-priority item while data changes.
If you only need one final sorted list, sort. If you need the next best item many times, use a heap.
Where heaps fit
A heap gives fast access to one extreme: min or max. In Python, heapq is a min-heap. In Java, PriorityQueue is a min-heap by default.
Common interview clues: kth largest, top K frequent, merge K sorted lists, meeting rooms, running median, shortest path later in graphs. The word priority may not appear.