Gather your supplies.
Remove bottle cap. It is important to use a bottle opener that will not bend or scar the cap. I found this kind of opener works best.
Pour beer. You'll need it!
You can add a magnet directly to the inside but I found the plastic seal frequently causes the magnet to sit cock-eyed.
Use the knife to pry up part of the seal and then put it all the way off.
Now you have a much more even surface to glue on.
One magnet isn't thick enough so I use two.
Put a healthy drop of glue in the cap.
Add one magnet and then place a small drop of glue on top of it.
Place the second magnet on top and then set aside to dry.
Finally, begin or add it to your collection!