After the purchase, the Code comes on email. Activation instructions:

Get the 16 digit code to email.

On your iPhone, iPad, or iPod touch, open the App Store app.

At the top of the screen, tap the sign in button or your photo.

Click Redeem Gift Card or Code. If you don't see Redeem a Gift Card or Code, sign in with your Apple ID.

With the card, you can pay for the purchase of games in the AppStore, add-ons, a subscription to iTunes, Apple Music Apple Arcade and Apple TV +

ATTENTION! This card is only suitable for Russian accounts (Russia region). The code can only be used once.

Official instructions for activating a gift card:
http://support.apple.com/kb/HT1574?viewlocale=ru_RU