All you need to do is point it at whatever mob you want to catch and fire it like you would a bow. The longer you hold the further the device will fire. It’s great for easily capturing farm animals like chickens, cows, sheep and horses.
But you can just as easily capture creepers, zombies, skeletons, and even endermen.
The great thing about this device is you can change it from capture to release by holding shift and right-clicking with the launcher in hand. Then fire it as you would in capture mode and it’ll release any of the mobs you’ve caught one by one. This is great for transferring animals to your farm.
You can even put the devices in a dispenser to set traps!