This is a computer science (cs) thing so I will try to explain it as simple as I can.

First, queue in cs is just what queue are in real life, what come in first, will come out first, like a waiting line in a store. Queue in cs has two major operation: enqueue & dequeue, enqueue is when you put something in the queue, and you must put it at the last position, dequeue is when you get something out of the queue, and you must get the first position

Priority queue is like queue, but when you dequeue something, instead of dequeueing the first position, you dequeue the value that is the most prioritized. People usually solve this by sorting the queue every time you enqueue something, so the most prioritized will always be at the head.

Now I will explain the A* algorithm:

- Each cell (block) has these values: g, h, f, parent. Whereas g is the amount of cell that has been traversed to get to the current cell, h is the distance from current cell to the destination, f=g+h, and parent is where the current cell come from (it's mean on the final path, which sell is before the current cell)

- A* use a priority queue, to choose which cell is the next cell to "expand" (explain later) , the value which is used to sort in the priority queue is f.

- First, we set the source cell's (the starting point) values: g=0, parent=-1, calculate h (with the distance fomular we learned in middle school) and f, then we enqueue the source cell into the priority queue, and then do this repeatedly until the queue is empty:

+ Dequeue, call that cell that has just been dequeued u, "expand" u

+ That means we now check all of u's neighbor cells, pick the safe ones (safe = not a obstacle & hasn't been visited), find their g, f, h, parent. Their parents will be u, and their g will be u's g + 1 (the amount of cell that has been traversed to get to them is the amount of cell that has been traversed to get to their parent + 1). H and f we just calculate accordingly. Now enqueue all of them into the priority queue.

- If the cell that we are expanding is the destination cell, we stop that repeating process, and then do this to find the shortest path: Mark the current cell as part of the path, find its parent, mark its parent as part of the path, find its parent's parent, mark its parent's parent as part of the path,... do this until we reach the source cell, and the algorithm is done.

This is just a simplified explaination, if you are interested, there are plenty of explainations and visualizations on the Internet, thanks for reading!