Lure Modules can be purchased from the game store with PokéCoins, and can be used to attract a large number of Pokémon to you. The bait lasts for 30 minutes, during which the attracted Pokémon can be seen not only by you, but also by other players nearby, so they can also catch them.
So, open the map, and then go to any PokéStop nearby.
Now notice the white little groove that looks like a pill just above the circular disc - this is your decoy module slot. Click on it and then click on the PokéStop module that you see at the bottom of the screen. After that, click on the decoy module to activate it.
Confirmation that the module is working are pink flowers like confetti falling around the PokéStop.
It is worth using the bait wisely, since it costs Pokécoins, and they, in turn, cost real money. However, if you take your time, you can always get PokéCoins without using microtransactions. To do this go to this guide.
