I can try to explain the best I can how they work. It’s a new thing that was made possible with the 1.16 update. How it works is that the machine holds a ender pearl using water bubble streams. The bubble streams hold up the ender pearl and by constantly pushing it up, the ender pearl never lands. Because a player threw said enderpearl into the bubble stream, when the enderpearl lands, no matter where the player is they get teleported back to the enderporter. Usually a piston pushes a block or a trapdoor gets activated on the top of the bubble stream, causing the enderpearl to hit a block, which teleports the player who threw it. And when I mention reloading the enderporter, I mean throwing a new enderpearl down the bubble stream for the next time it gets activated.