You throw an item or block into the hopper and get another item in return.

In the picture, it is not a fountain, as a fountain traditionally contains water. If you want to experience the "wishing well" feeling, you can also build the funnel in the middle one block deeper and put a block of water on it.
The wishing well works on the system that items thrown in at the bottom are brought up to a dropper by goods lore, so that the supply of items there is never exhausted.
So the content of the dropper depends on the items thrown in. So the player can decide for himself if he wants to give something more generous to the next player or not. You can also throw in several items at the same time, but only one item will be thrown out at a time.

Instructions:

If you understand how it works and know a bit about Redstone, the setup isn't terribly complicated.

On the picture it is two funnels below each other, so that the comparator can be placed next to it. You can also omit the upper funnel or replace it with water.
Dropper there are also two pieces under each other, so that you do not get to the dropper that contains all the items.
When building the acceleration tracks, keep in mind that the top of the lorry should travel as slowly as possible so that as many items as possible can pass through the funnel if someone ever throws in multiple items.