First things first, you need to find and tap on the Game Center app. Once you're inside, make sure you're logged in and then tap on the 'Games' tab along the bottom.
You'll be presented with a list of every Game Center-compatible app you've ever opened.
For the purposes of this how to, we'll pick Ubisoft's auto-running platform gem Rayman Jungle Run. Let's get challenging.
You'll be presented with the game's leaderboards. Pick the level or race track that you think you're best at, and then - on the next page - tap on your own high score (called 'Me', suitably).
You'll reach the screen on the left. Hit 'Challenge Friends', and then you'll be presented with a list of Game Center pals - split between people who have the game in question, and those who don't.
You can choose multiple friends, with tick boxes included down the left-hand column.
When you're ready to rumble, hit 'Next', compose an optional message ("come and have a go if you're think you're hard enough" works well), and hit 'Send'.
All of the players mentioned in the previous step will now receive a notification on their iOS device letting them know they have been challenged.
If you're not up to the task, you can wuss out and hit 'Decline'. If you're feeling competitive, on the other hand, hit 'Play Now'. This will launch the game in question - but, you'll need to find the level or race by yourself.
Good luck - your reputation is on the line!
If you win, you'll be greeted with a pop-up notification from Game Center declaring you the victor. Even better: the person who sent the challenge will get a push notification with word of your victory, totally rubbing it in his stupid face.
It also automatically starts a new challenge, with the newly set time now the benchmark. This eternal one-upmanship only ends when one player declines the challenge, or dies.
Game Center challenges also work with achievements. Pick achievements instead of leaderboards on the game's page, tap on an achievement you own (and are proud of grabbing), and then choose some challenge friends.
As ever, you can select multiple pals and send out a goading message. And, yes, you will receive a notification if your buddy grabs the trophy.