Q: i don't no about redeem code

Redemption codes are codes you can obtain to claim rewards, they can be for apps, credit, music, movies and virtually anything in the Apple App Store/iTunes store. If you want to know how to claim redemption codes, here is an article about how to redeem them. As for why it pops up, perhaps you accidentally clicked on "redeem" which is located as highlighted by a red box in the image below.