In Battle Gem Ponies you capture the magical essence of a wild pony and keep it inside of something called a Command Gem. You use this Command Gem to transform your pony into whatever pony/stat/moveset combination you want. You have a pony trainer device that holds up to 3 of these Command Gems. The device takes the unique signature of the gem and transfers it to your pony, allowing you to swap through forms as if the device were a TV remote.
To claim a wild pony's signature for your own pony you'll need to use that same device to scan, copy, then print the signature onto empty Command Gems called Capture Gems. Once a Capture Gem holds a pony's signature, it becomes a Command Gem.
Capture Gems come in a number of different forms and using the right kind under the right circumstances makes the capture process much easier. Get a list of all the different ones over here.
